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, 2018	42,505
Balance at Dec. 31, 2018	$ 450,908	$ 194,728	$ (5,543)	$ 640,093
Net income	0	46,874	0	46,874
Other comprehensive income (loss)	0	0	1,405	1,405
Dividends and dividend equivalents declared	$ 0	(37,069)	0	(37,069)
Common stock issued under the employee equity incentive plan (in shares)	715
Common stock issued under the employee equity incentive plan	$ 12,471	0	0	12,471
Stock-based compensation expense	$ 38,753	0	0	38,753
Balance (in shares) at Jun. 30, 2019	43,234
Balance at Jun. 30, 2019	$ 503,759	204,533	(4,138)	704,154
Common stock issued under the employee stock purchase plan (in shares)	14
Common stock issued under the employee stock purchase plan	$ 1,627	0	0	1,627
Balance (in shares) at Mar. 31, 2019	43,033
Balance at Mar. 31, 2019	$ 478,913	202,378	(1,040)	680,251
Net income	0	20,693	0	20,693
Other comprehensive income (loss)	0	0	(3,098)	(3,098)
Dividends and dividend equivalents declared	$ 0	(18,538)	0	(18,538)
Common stock issued under the employee equity incentive plan (in shares)	201
Common stock issued under the employee equity incentive plan	$ 2,088	0	0	2,088
Stock-based compensation expense	$ 22,758	0	0	22,758
Balance (in shares) at Jun. 30, 2019	43,234
Balance at Jun. 30, 2019	$ 503,759	204,533	(4,138)	$ 704,154
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	65,922	0	65,922
Other comprehensive income (loss)	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			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 (loss)	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			44,911
Balance at Jun. 30, 2020	$ 605,165	$ 247,864	$ (4,084)	$ 848,945