Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock Including Additional Paid in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2016	40,793
Balance at Dec. 31, 2016	$ 315,969	$ 119,362	$ (4,215)	$ 431,116
Net income	0	65,203	0	65,203
Other comprehensive income (loss)	0	0	6,028	6,028
Dividends and dividend equivalents declared	$ 0	(35,816)	0	(35,816)
Common stock issued under the employee equity incentive plan (in shares)	781
Common stock issued under the employee equity incentive plan	$ 150	0	0	150
Common stock issued under the employee stock purchase plan (in shares)	40
Common stock issued under the employee stock purchase plan	$ 2,701	0	0	2,701
Stock-based compensation expense	52,625	0	0	52,625
Cumulative effect of a change in accounting principles at Dec. 31, 2017	$ 5,141	(5,141)	0	0
Balance (in shares) at Dec. 31, 2017	41,614
Balance at Dec. 31, 2017	$ 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
Cumulative effect of a change in accounting principles at Dec. 31, 2018	$ 0	379	0	$ 379
Balance (in shares) at Dec. 31, 2018	42,505			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