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	35,756	0	35,756
Other comprehensive 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
Balance at Mar. 31, 2020	$ 581,736	241,465	(10,011)	$ 813,190
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	45,413	0	45,413
Other comprehensive loss	0	0	(3,128)	(3,128)
Dividends and dividend equivalents declared	$ 0	(28,953)	0	(28,953)
Common stock issued under the employee equity incentive plan (in shares)	460
Common stock issued under the employee equity incentive plan	$ 10,744	0	0	10,744
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
Stock-based compensation expense	$ 28,621	0	0	$ 28,621
Balance (in shares) at Mar. 31, 2021	45,737			45,737
Balance at Mar. 31, 2021	$ 699,359	$ 315,206	$ 7,012	$ 1,021,577