Consolidated Statements of Stockholders' Equity (unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Beginning Balance at Dec. 31, 2018	$ 986,989	$ 355		$ 323,622	$ (41,653)	$ 704,665
Beginning Balance, Shares at Dec. 31, 2018		35,482
Issuance of common stock under employee stock plans, net of shares withheld for payroll taxes, Value	(6,419)	$ 3		(6,422)
Issuance of common stock under employee stock plans, net of shares withheld for payroll taxes, Shares		310
Stock-based compensation expense	11,895			11,895
Equity component of convertible senior notes, net of deferred tax of $14,819 and issuance costs of $1,700	44,731			44,731
Issuance of warrants related to convertible senior notes	34,440			34,440
Purchase of note hedge related to convertible senior notes, net of deferred tax of $16,047	(50,278)			(50,278)
Repurchase of treasury stock	(27,899)		$ (27,899)
Repurchase of treasury stock, Shares			541
Retirement of treasury stock, Amount		$ (5)	$ 27,899	(4,919)		(22,975)
Retirement of treasury stock, Shares		541	(541)
Foreign currency translation adjustments, net of tax	(7,278)				(7,278)
Net earnings	116,457					116,457
Ending Balance at Sep. 30, 2019	1,102,638	$ 353		353,069	(48,931)	798,147
Ending Balance, Shares at Sep. 30, 2019		35,251
Beginning Balance at Jun. 30, 2019	1,079,583	$ 358		325,263	(40,028)	793,990
Beginning Balance, Shares at Jun. 30, 2019		35,781
Issuance of common stock under employee stock plans, net of shares withheld for payroll taxes, Value	(266)			(266)
Issuance of common stock under employee stock plans, net of shares withheld for payroll taxes, Shares		11
Stock-based compensation expense	4,098			4,098
Equity component of convertible senior notes, net of deferred tax of $14,819 and issuance costs of $1,700	44,731			44,731
Issuance of warrants related to convertible senior notes	34,440			34,440
Purchase of note hedge related to convertible senior notes, net of deferred tax of $16,047	(50,278)			(50,278)
Repurchase of treasury stock	(27,899)		$ (27,899)
Repurchase of treasury stock, Shares			541
Retirement of treasury stock, Amount		$ (5)	$ 27,899	(4,919)		(22,975)
Retirement of treasury stock, Shares		541	(541)
Foreign currency translation adjustments, net of tax	(8,903)				(8,903)
Net earnings	27,132					27,132
Ending Balance at Sep. 30, 2019	1,102,638	$ 353		353,069	(48,931)	798,147
Ending Balance, Shares at Sep. 30, 2019		35,251
Beginning Balance at Dec. 31, 2019	1,160,318	$ 353		357,032	(38,164)	841,097
Beginning Balance, Shares at Dec. 31, 2019		35,263
Issuance of common stock under employee stock plans, net of shares withheld for payroll taxes, Value	(5,713)	$ 2		(5,715)
Issuance of common stock under employee stock plans, net of shares withheld for payroll taxes, Shares		272
Stock-based compensation expense	11,754			11,754
Repurchase of treasury stock	(25,000)		$ (25,000)
Repurchase of treasury stock, Shares			(445)
Retirement of treasury stock, Amount		$ (4)	$ 25,000	(4,504)		(20,492)
Retirement of treasury stock, Shares		(445)	445
Foreign currency translation adjustments, net of tax	2,280				2,280
Net earnings	119,252					119,252
Ending Balance at Sep. 30, 2020	1,262,891	$ 351		358,567	(35,884)	939,857
Ending Balance, Shares at Sep. 30, 2020		35,090
Beginning Balance at Jun. 30, 2020	1,207,356	$ 351		354,431	(48,376)	900,950
Beginning Balance, Shares at Jun. 30, 2020		35,070
Issuance of common stock under employee stock plans, net of shares withheld for payroll taxes, Value	(376)			(377)		1
Issuance of common stock under employee stock plans, net of shares withheld for payroll taxes, Shares		20
Stock-based compensation expense	4,513			4,513
Foreign currency translation adjustments, net of tax	12,492				12,492
Net earnings	38,906					38,906
Ending Balance at Sep. 30, 2020	$ 1,262,891	$ 351		$ 358,567	$ (35,884)	$ 939,857
Ending Balance, Shares at Sep. 30, 2020		35,090