Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member] Common Class A [Member]	Common Stock [Member] Common Class B [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2012	27,999,000	10,792,000
Balance at Dec. 31, 2012			$ 404	$ 222,627	$ (17,948)	$ 404,619	$ (1,756)	$ 607,946
Stock options exercised and stock awards (including tax benefit of $2,566) (in shares)	747,000	43,000
Stock options exercised and stock awards			$ 8	11,325				11,333
Stock-based compensation related to stock options, restricted shares and employee stock purchase plan				8,645				8,645
Vesting of restricted share awards (in shares)	85,000	24,000
Vesting of restricted share awards			$ 1	(711)				(710)
Stock Issued During Period, Shares, Employee Stock Purchase Plans	80,000
Issuance of common stock under employee stock purchase plan			$ 1	$ 1,268				1,269
Common stock repurchases (in shares)		(554,000)
Common stock repurchases					$ (12,873)			(12,873)
Other comprehensive income							$ 554	554
Net income						$ 49,217		49,217
Balance (in shares) at Dec. 31, 2013	28,911,000	10,305,000
Balance at Dec. 31, 2013			$ 414	$ 243,154	$ (30,821)	$ 453,836	$ (1,202)	665,381
Stock options exercised and stock awards (including tax benefit of $2,566) (in shares)	872,000	30,000
Stock options exercised and stock awards			$ 9	16,216				16,225
Stock-based compensation related to stock options, restricted shares and employee stock purchase plan				11,343				11,343
Vesting of restricted share awards (in shares)	42,000	113,000
Vesting of restricted share awards			$ 1	311				312
Stock Issued During Period, Shares, Employee Stock Purchase Plans	64,000
Issuance of common stock under employee stock purchase plan				$ 1,462				1,462
Common stock repurchases (in shares)		(449,000)
Common stock repurchases					$ (12,253)			(12,253)
Other comprehensive income							$ 742	742
Net income						$ 79,957		79,957
Balance (in shares) at Dec. 31, 2014	29,889,000	9,999,000
Balance at Dec. 31, 2014			$ 424	$ 272,486	$ (41,904)	$ 533,793	$ (460)	764,339
Issuance of common stock related to business acquisition					$ 1,170			$ 1,170
Stock options exercised and stock awards (including tax benefit of $2,566) (in shares)	182,000							182,199
Stock options exercised and stock awards			$ 2	$ 1,933				$ 1,935
Stock-based compensation related to stock options, restricted shares and employee stock purchase plan				12,384				12,384
Vesting of restricted share awards (in shares)	147,000	150,000
Vesting of restricted share awards			$ 3	(572)				(569)
Stock Issued During Period, Shares, Employee Stock Purchase Plans	86,000
Issuance of common stock under employee stock purchase plan			$ 1	$ 2,063				2,064
Common stock repurchases (in shares)		(56,000)
Common stock repurchases					$ (1,464)			(1,464)
Other comprehensive income							$ 155	155
Net income						$ 66,053		66,053
Balance (in shares) at Dec. 31, 2015	30,304,000	10,093,000
Balance at Dec. 31, 2015			$ 430	$ 288,294	$ (43,368)	$ 599,846	$ (305)	$ 844,897