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	26,181	0	26,181
Other comprehensive income (loss)	0	0	4,503	4,503
Dividends and dividend equivalents declared	$ 0	(18,531)	0	(18,531)
Common stock issued under the employee equity incentive plan (in shares)	514
Common stock issued under the employee equity incentive plan	$ 10,383	0	0	10,383
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
Stock-based compensation expense	$ 15,995	0	0	15,995
Balance (in shares) at Mar. 31, 2019	43,033
Balance at Mar. 31, 2019	$ 478,913	202,378	(1,040)	$ 680,251
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	35,756	0	35,756
Other comprehensive income (loss)	0	0	(4,535)	(4,535)
Dividends and dividend equivalents declared	$ 0	(23,741)	0	(23,741)
Common stock issued under the employee equity incentive plan (in shares)	1,084
Common stock issued under the employee equity incentive plan	$ 11,758	0	0	11,758
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
Stock-based compensation expense	$ 18,569	0	0	$ 18,569
Balance (in shares) at Mar. 31, 2020	44,715			44,715
Balance at Mar. 31, 2020	$ 581,736	$ 241,465	$ (10,011)	$ 813,190