Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance as of January 1, 2012 at Dec. 31, 2011	$ 159,336	$ 79,948	$ 3,593	$ 242,877
Balance as of January 1, 2012 (in Shares) at Dec. 31, 2011	33,826,000
Net income		15,756		15,756
Other comprehensive income			582	582
Dividends		(35,664)		(35,664)
Exercise of stock options and related tax benefits	14,232			14,232
Exercise of stock options and related tax benefits (in Shares)	1,152,000			1,152,000
Shares issued under the employee stock purchase plan	1,852			1,852
Shares issued under the employee stock purchase plan (in Shares)	152,000
Stock-based compensation expense	18,659			18,659
Release of restricted stock (in Shares)	543,000
Balance as of at Dec. 31, 2012	194,079	60,040	4,175	258,294
Balance as of (in Shares) at Dec. 31, 2012	35,673,000
Net income		22,898		22,898
Other comprehensive income			2,085	2,085
Exercise of stock options and related tax benefits	37,877			37,877
Exercise of stock options and related tax benefits (in Shares)	2,446,000			2,446,000
Repurchase of common shares	(20,615)			(20,615)
Repurchase of common shares (in Shares)	(664,000)
Shares issued under the employee stock purchase plan	2,145			2,145
Shares issued under the employee stock purchase plan (in Shares)	111,000
Stock-based compensation expense	20,715			20,715
Release of restricted stock (in Shares)	725,000
Balance as of at Dec. 31, 2013	234,201	82,938	6,260	323,399
Balance as of (in Shares) at Dec. 31, 2013	38,291,000			38,291,000
Net income		35,495		35,495
Other comprehensive income			(449)	(449)
Dividends		(18,319)		(18,319)
Exercise of stock options and related tax benefits	11,960			11,960
Exercise of stock options and related tax benefits (in Shares)	742,000			742,000
Repurchase of common shares	(41,198)			(41,198)
Repurchase of common shares (in Shares)	(1,051,000)
Shares issued under the employee stock purchase plan	2,078			2,078
Shares issued under the employee stock purchase plan (in Shares)	78,000
Stock-based compensation expense	33,459			33,459
Release of restricted stock (in Shares)	772,000
Balance as of at Dec. 31, 2014	$ 240,500	$ 100,114	$ 5,811	$ 346,425
Balance as of (in Shares) at Dec. 31, 2014	38,832,000			38,832,000