Investments - Schedule of Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Available-for-sale securities:
Short-term investments, Amortized Cost	$ 492,375	$ 459,123
Gross Unrealized Gains	2,300	1,525
Gross Unrealized Losses less than one year	(12)	(116)
Gross Unrealized Losses greater than one year	(26)	(347)
Short-term investments, Estimated Fair Value	494,665	460,522
Long-term investments, Amortized Cost	27,752	73,340
Total long-term investments	27,869	73,148
Long-term investments, Estimated Fair Value	27,724	73,003
Amortized Cost	520,272	532,608
Estimated Fair Value	522,534	533,670
Short-term investments
Available-for-sale securities:
Gross Unrealized Gains	2,300	1,525
Gross Unrealized Losses less than one year	(3)	(116)
Gross Unrealized Losses greater than one year	(7)	(10)
Long-term investments
Available-for-sale securities:
Gross Unrealized Losses less than one year	(9)
Gross Unrealized Losses greater than one year	(19)	(337)
Total long-term investments	27,869	73,148
Amortized Cost	27,897	73,485
Certificates of deposit
Available-for-sale securities:
Amortized Cost	145	145
Estimated Fair Value	145	145
Corporate debt securities
Available-for-sale securities:
Short-term investments, Amortized Cost	218,685	192,617
Short-term investments, Estimated Fair Value	219,952	193,317
Long-term investments, Amortized Cost	17,690	24,484
Long-term investments, Estimated Fair Value	17,672	24,326
Corporate debt securities \| Short-term investments
Available-for-sale securities:
Gross Unrealized Gains	1,268	762
Gross Unrealized Losses less than one year		(58)
Gross Unrealized Losses greater than one year	(1)	(4)
Corporate debt securities \| Long-term investments
Available-for-sale securities:
Gross Unrealized Losses less than one year	(5)
Gross Unrealized Losses greater than one year	(13)	(158)
U.S. government and agency debt securities
Available-for-sale securities:
Short-term investments, Amortized Cost	273,690	266,506
Short-term investments, Estimated Fair Value	274,713	267,205
Long-term investments, Amortized Cost	10,062	48,856
Long-term investments, Estimated Fair Value	10,052	48,677
U.S. government and agency debt securities \| Short-term investments
Available-for-sale securities:
Gross Unrealized Gains	1,032	763
Gross Unrealized Losses less than one year	(3)	(58)
Gross Unrealized Losses greater than one year	(6)	(6)
U.S. government and agency debt securities \| Long-term investments
Available-for-sale securities:
Gross Unrealized Losses less than one year	(4)
Gross Unrealized Losses greater than one year	$ (6)	$ (179)

Alkermes plc. 10-Q