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	76,402	0	76,402
Other comprehensive income (loss)	0	0	(4,496)	(4,496)
Dividends and dividend equivalents declared	$ 0	(55,438)	0	(55,438)
Common stock issued under the employee equity incentive plan (in shares)	902
Common stock issued under the employee equity incentive plan	$ 14,561	0	0	14,561
Common stock issued under the employee stock purchase plan (in shares)	28
Common stock issued under the employee stock purchase plan	$ 3,277	0	0	3,277
Stock-based compensation expense	$ 60,029	0	0	60,029
Balance (in shares) at Sep. 30, 2019	43,435
Balance at Sep. 30, 2019	$ 528,775	215,692	(10,039)	734,428
Balance (in shares) at Jun. 30, 2019	43,234
Balance at Jun. 30, 2019	$ 503,759	204,533	(4,138)	704,154
Net income	0	29,528	0	29,528
Other comprehensive income (loss)	0	0	(5,901)	(5,901)
Dividends and dividend equivalents declared	$ 0	(18,369)	0	(18,369)
Common stock issued under the employee equity incentive plan (in shares)	187
Common stock issued under the employee equity incentive plan	$ 2,090	0	0	2,090
Common stock issued under the employee stock purchase plan (in shares)	14
Common stock issued under the employee stock purchase plan	$ 1,650	0	0	1,650
Stock-based compensation expense	$ 21,276	0	0	21,276
Balance (in shares) at Sep. 30, 2019	43,435
Balance at Sep. 30, 2019	$ 528,775	215,692	(10,039)	$ 734,428
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	121,488	0	121,488
Other comprehensive income (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			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 income (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			45,096
Balance at Sep. 30, 2020	$ 632,432	$ 279,653	$ 2,484	$ 914,569