Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Cumulative Effect, Period of Adoption, Adjustment [Member] Common Stock Including Additional Paid in Capital [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] AOCI Attributable to Parent [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock Including Additional Paid in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2017					41,614
Balance at Dec. 31, 2017	$ 0	$ 379	$ 0	$ 379	$ 376,586	$ 143,608	$ 1,813	$ 522,007
Net income					0	105,268	0	105,268
Other comprehensive income (loss)					0	0	(7,356)	(7,356)
Dividends and dividend equivalents declared					$ 0	(54,527)	0	(54,527)
Common stock issued under the employee equity incentive plan (in shares)					858
Common stock issued under the employee equity incentive plan					$ 10,637	0	0	10,637
Common stock issued under the employee stock purchase plan (in shares)					33
Common stock issued under the employee stock purchase plan					$ 3,028	0	0	3,028
Stock-based compensation expense					$ 60,657	0	0	60,657
Balance (in shares) at Dec. 31, 2018					42,505
Balance at Dec. 31, 2018					$ 450,908	194,728	(5,543)	640,093
Net income					0	108,839	0	108,839
Other comprehensive income (loss)					0	0	67	67
Dividends and dividend equivalents declared					$ 0	(74,117)	0	(74,117)
Common stock issued under the employee equity incentive plan (in shares)					1,083
Common stock issued under the employee equity incentive plan					$ 16,650	0	0	16,650
Common stock issued under the employee stock purchase plan (in shares)					28
Common stock issued under the employee stock purchase plan					$ 3,277	0	0	3,277
Stock-based compensation expense					$ 78,682	0	0	$ 78,682
Balance (in shares) at Dec. 31, 2019					43,616			43,616
Balance at Dec. 31, 2019					$ 549,517	229,450	(5,476)	$ 773,491
Net income					0	164,375	0	164,375
Other comprehensive income (loss)					0	0	15,616	15,616
Dividends and dividend equivalents declared					$ 0	(95,079)	0	(95,079)
Common stock issued under the employee equity incentive plan (in shares)					1,623
Common stock issued under the employee equity incentive plan					$ 18,767	0	0	18,767
Common stock issued under the employee stock purchase plan (in shares)					28
Common stock issued under the employee stock purchase plan					$ 3,819	0	0	3,819
Stock-based compensation expense					$ 85,598	0	0	$ 85,598
Balance (in shares) at Dec. 31, 2020					45,267			45,267
Balance at Dec. 31, 2020					$ 657,701	$ 298,746	$ 10,140	$ 966,587