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	65,922	0	65,922
Other comprehensive income	0	0	1,392	1,392
Dividends and dividend equivalents declared	$ 0	(47,508)	0	(47,508)
Common stock issued under the employee equity incentive plan (in shares)	1,280
Common stock issued under the employee equity incentive plan	$ 14,110	0	0	14,110
Stock-based compensation expense	$ 39,646	0	0	39,646
Balance (in shares) at Jun. 30, 2020	44,911
Balance at Jun. 30, 2020	$ 605,165	247,864	(4,084)	848,945
Common stock issued under the employee stock purchase plan (in shares)	15
Common stock issued under the employee stock purchase plan	$ 1,892	0	0	1,892
Balance (in shares) at Mar. 31, 2020	44,715
Balance at Mar. 31, 2020	$ 581,736	241,465	(10,011)	813,190
Net income	0	30,167	0	30,167
Other comprehensive income	0	0	5,927	5,927
Dividends and dividend equivalents declared	$ 0	(23,768)	0	(23,768)
Common stock issued under the employee equity incentive plan (in shares)	196
Common stock issued under the employee equity incentive plan	$ 2,352	0	0	2,352
Stock-based compensation expense	$ 21,077	0	0	21,077
Balance (in shares) at Jun. 30, 2020	44,911
Balance at Jun. 30, 2020	$ 605,165	247,864	(4,084)	$ 848,945
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	100,582	0	100,582
Other comprehensive income	0	0	2,161	2,161
Dividends and dividend equivalents declared	$ 0	(57,946)	0	(57,946)
Common stock issued under the employee equity incentive plan (in shares)	640
Common stock issued under the employee equity incentive plan	$ 12,920	0	0	12,920
Stock-based compensation expense	$ 60,758	0	0	$ 60,758
Balance (in shares) at Jun. 30, 2021	45,917			45,917
Balance at Jun. 30, 2021	$ 733,672	341,382	12,301	$ 1,087,355
Common stock issued under the employee stock purchase plan (in shares)	10
Common stock issued under the employee stock purchase plan	$ 2,293	0	0	2,293
Balance (in shares) at Mar. 31, 2021	45,737
Balance at Mar. 31, 2021	$ 699,359	315,206	7,012	1,021,577
Net income	0	55,169	0	55,169
Other comprehensive income	0	0	5,289	5,289
Dividends and dividend equivalents declared	$ 0	(28,993)	0	(28,993)
Common stock issued under the employee equity incentive plan (in shares)	180
Common stock issued under the employee equity incentive plan	$ 2,176	0	0	2,176
Stock-based compensation expense	$ 32,137	0	0	$ 32,137
Balance (in shares) at Jun. 30, 2021	45,917			45,917
Balance at Jun. 30, 2021	$ 733,672	$ 341,382	$ 12,301	$ 1,087,355