Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - 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, 2019	43,616
Balance at Dec. 31, 2019	$ 549,517	$ 229,450	$ (5,476)	$ 773,491
Net income	0	121,488	0	121,488
Other comprehensive loss	0	0	7,960	7,960
Dividends and dividend equivalents declared	$ 0	(71,285)	0	(71,285)
Common stock issued under the employee equity incentive plan (in shares)	1,452
Common stock issued under the employee equity incentive plan	$ 16,457	0	0	16,457
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	$ 62,639	0	0	62,639
Balance (in shares) at Sep. 30, 2020	45,096
Balance at Sep. 30, 2020	$ 632,432	279,653	2,484	914,569
Balance (in shares) at Jun. 30, 2020	44,911
Balance at Jun. 30, 2020	$ 605,165	247,864	(4,084)	848,945
Net income	0	55,566	0	55,566
Other comprehensive loss	0	0	6,568	6,568
Dividends and dividend equivalents declared	$ 0	(23,777)	0	(23,777)
Common stock issued under the employee equity incentive plan (in shares)	173
Common stock issued under the employee equity incentive plan	$ 2,347	0	0	2,347
Common stock issued under the employee stock purchase plan (in shares)	12
Common stock issued under the employee stock purchase plan	$ 1,927	0	0	1,927
Stock-based compensation expense	$ 22,993	0	0	22,993
Balance (in shares) at Sep. 30, 2020	45,096
Balance at Sep. 30, 2020	$ 632,432	279,653	2,484	$ 914,569
Balance (in shares) at Dec. 31, 2020	45,267			45,267
Balance at Dec. 31, 2020	$ 657,701	298,746	10,140	$ 966,587
Net income	0	169,352	0	169,352
Other comprehensive loss	0	0	1,522	1,522
Dividends and dividend equivalents declared	$ 0	(86,905)	0	(86,905)
Common stock issued under the employee equity incentive plan (in shares)	807
Common stock issued under the employee equity incentive plan	$ 15,147	0	0	15,147
Common stock issued under the employee stock purchase plan (in shares)	17
Common stock issued under the employee stock purchase plan	$ 4,670	0	0	4,670
Stock-based compensation expense	$ 92,340	0	0	$ 92,340
Balance (in shares) at Sep. 30, 2021	46,091			46,091
Balance at Sep. 30, 2021	$ 769,858	381,193	11,662	$ 1,162,713
Balance (in shares) at Jun. 30, 2021	45,917
Balance at Jun. 30, 2021	$ 733,672	341,382	12,301	1,087,355
Net income	0	68,770	0	68,770
Other comprehensive loss	0	0	(639)	(639)
Dividends and dividend equivalents declared	$ 0	(28,959)	0	(28,959)
Common stock issued under the employee equity incentive plan (in shares)	167
Common stock issued under the employee equity incentive plan	$ 2,227	0	0	2,227
Common stock issued under the employee stock purchase plan (in shares)	7
Common stock issued under the employee stock purchase plan	$ 2,377	0	0	2,377
Stock-based compensation expense	$ 31,582	0	0	$ 31,582
Balance (in shares) at Sep. 30, 2021	46,091			46,091
Balance at Sep. 30, 2021	$ 769,858	$ 381,193	$ 11,662	$ 1,162,713