Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock Voting	Additional Paid In Capital	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Retained Earnings
Beginning balance (in shares) at Mar. 31, 2019		119,760,132			42,149,771
Beginning balance at Mar. 31, 2019	$ 2,065,433	$ 120	$ 2,828,922	$ (2,639)	$ (1,119,063)	$ 358,093
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(10,090)					(10,090)
Unrealized net investment gains (losses)	40			40
Unrealized net gains on derivative financial instruments	43			43
Cumulative translation adjustments	(789)			(789)
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		1,621,350
Issuance of common stock pursuant to vesting of restricted stock units	2	$ 2
Stock-based compensation expense for restricted stock units granted to employees	38,187		38,187
Issuance of common stock under employee stock purchase plan (in shares)		297,635
Issuance of common stock under employee stock purchase plan	6,593		6,593
Repurchase of treasury stock (in shares)					5,674,125
Repurchase of treasury stock	(136,612)				$ (136,612)
Ending balance (in shares) at Dec. 31, 2019		121,679,117			47,823,896
Ending balance at Dec. 31, 2019	1,962,807	$ 122	2,873,702	(3,345)	$ (1,255,675)	348,003
Beginning balance (in shares) at Sep. 30, 2019		121,648,747			46,810,700
Beginning balance at Sep. 30, 2019	1,940,264	$ 122	2,863,003	(3,699)	$ (1,230,440)	311,278
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	36,725					36,725
Unrealized net investment gains (losses)	3			3
Unrealized net gains on derivative financial instruments	54			54
Cumulative translation adjustments	297			297
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		30,370
Issuance of common stock pursuant to vesting of restricted stock units	0
Stock-based compensation expense for restricted stock units granted to employees	10,699		10,699
Repurchase of treasury stock (in shares)					1,013,196
Repurchase of treasury stock	(25,235)				$ (25,235)
Ending balance (in shares) at Dec. 31, 2019		121,679,117			47,823,896
Ending balance at Dec. 31, 2019	1,962,807	$ 122	2,873,702	(3,345)	$ (1,255,675)	348,003
Beginning balance (in shares) at Mar. 31, 2020		122,006,077			49,785,171
Beginning balance at Mar. 31, 2020	1,937,919	$ 122	2,891,553	(3,160)	$ (1,305,935)	355,339
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	7,915					7,915
Unrealized net investment gains (losses)	(122)			(122)
Unrealized net gains on derivative financial instruments	169			169
Cumulative translation adjustments	3,375			3,375
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		1,581,484
Issuance of common stock pursuant to vesting of restricted stock units	2	$ 2
Stock-based compensation expense for restricted stock units granted to employees	38,545		38,545
Issuance of common stock under employee stock purchase plan (in shares)		279,812
Issuance of common stock under employee stock purchase plan	6,475		6,475
Repurchase of treasury stock (in shares)					644,178
Repurchase of treasury stock	(16,043)				$ (16,043)
Ending balance (in shares) at Dec. 31, 2020		123,867,373			50,429,349
Ending balance at Dec. 31, 2020	1,978,235	$ 124	2,936,573	262	$ (1,321,978)	363,254
Beginning balance (in shares) at Sep. 30, 2020		123,840,945			50,266,910
Beginning balance at Sep. 30, 2020	1,939,320	$ 123	2,924,757	(1,258)	$ (1,318,535)	334,233
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	29,021					29,021
Unrealized net investment gains (losses)	(15)			(15)
Unrealized net gains on derivative financial instruments	53			53
Cumulative translation adjustments	1,482			1,482
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		26,428
Issuance of common stock pursuant to vesting of restricted stock units	1	$ 1
Stock-based compensation expense for restricted stock units granted to employees	11,816		11,816
Repurchase of treasury stock (in shares)					162,439
Repurchase of treasury stock	(3,443)				$ (3,443)
Ending balance (in shares) at Dec. 31, 2020		123,867,373			50,429,349
Ending balance at Dec. 31, 2020	$ 1,978,235	$ 124	$ 2,936,573	$ 262	$ (1,321,978)	$ 363,254