Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2014	38,832
Balance at Dec. 31, 2014	$ 240,500	$ 100,114	$ 5,811	$ 346,425
Net income		35,172		35,172
Other comprehensive gain (loss)			(4,345)	(4,345)
Dividends and dividend equivalents declared		(33,999)		$ (33,999)
Exercise of stock options (in shares)	498			498
Exercise of stock options	$ 7,744			$ 7,744
Release of restricted stock units (in shares)	948
Repurchase of common shares (in shares)	(645)
Repurchase of common shares	$ (32,286)			(32,286)
Shares issued under the employee stock purchase plan (in shares)	56
Shares issued under the employee stock purchase plan	$ 2,227			2,227
Stock-based compensation expense	41,650			41,650
Tax benefits from equity awards	$ 5,928			5,928
Balance (in shares) at Dec. 31, 2015	39,689
Balance at Dec. 31, 2015	$ 265,763	101,287	1,466	368,516
Net income		52,720		52,720
Other comprehensive gain (loss)			(5,681)	(5,681)
Dividends and dividend equivalents declared		(34,645)		$ (34,645)
Exercise of stock options (in shares)	76			76
Exercise of stock options	$ 1,344			$ 1,344
Release of restricted stock units (in shares)	975
Shares issued under the employee stock purchase plan (in shares)	53
Shares issued under the employee stock purchase plan	$ 2,463			2,463
Stock-based compensation expense	44,934			44,934
Tax benefits from equity awards	$ 1,465			$ 1,465
Balance (in shares) at Dec. 31, 2016	40,793			40,793
Balance at Dec. 31, 2016	$ 315,969	119,362	(4,215)	$ 431,116
Net income		65,203		65,203
Other comprehensive gain (loss)			6,028	6,028
Dividends and dividend equivalents declared		(35,816)		$ (35,816)
Exercise of stock options (in shares)	9			9
Exercise of stock options	$ 150			$ 150
Release of restricted stock units (in shares)	772
Shares issued under the employee stock purchase plan (in shares)	40
Shares issued under the employee stock purchase plan	$ 2,701			2,701
Stock-based compensation expense	$ 52,625			$ 52,625
Balance (in shares) at Dec. 31, 2017	41,614			41,614
Balance at Dec. 31, 2017	$ 376,586	143,608	1,813	$ 522,007
Cumulative-effect adjustment from adoption of ASU No. 2016-09	$ 5,141	$ (5,141)