Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2012	$ 364,738	$ 85,342	$ 279,396
Balance, Shares at Dec. 31, 2012		24,931,000
Net income	43,397		43,397
Share-based compensation	3,680	$ 3,680
Common stock issued under stock plans, net of shares withheld for employee taxes	15,067	$ 15,067
Common stock issued under stock Plans, net of shares withheld for employee taxes, Shares		826,000
Excess tax benefit (shortfall) from equity awards	1,329	$ 1,329
Taxes paid related to net share settlement of stock awards	(2,395)	(2,395)
Dividends accrued of $0.96, $0.98, $1.00 per share in 2013,2014 and 2015	(24,755)		(24,755)
Other comprehensive (loss) gain	(31)			$ (31)
Balance at Dec. 31, 2013	401,030	$ 103,023	298,038	(31)
Balance, Shares at Dec. 31, 2013		25,757,000
Net income	7,871
Balance at Mar. 31, 2014	401,563
Balance at Dec. 31, 2013	401,030	$ 103,023	298,038	(31)
Balance, Shares at Dec. 31, 2013		25,757,000
Net income	45,709		45,709
Share-based compensation	3,854	$ 3,854
Common stock issued under stock plans, net of shares withheld for employee taxes	$ 1,729	$ 1,729
Common stock issued under stock Plans, net of shares withheld for employee taxes, Shares		294,000
Common stock repurchased, Shares	0
Excess tax benefit (shortfall) from equity awards	$ 1,822	$ 1,822
Taxes paid related to net share settlement of stock awards	(3,959)	(3,959)
Dividends accrued of $0.96, $0.98, $1.00 per share in 2013,2014 and 2015	(25,583)		(25,583)
Other comprehensive (loss) gain	(71)			(71)
Balance at Dec. 31, 2014	$ 424,531	$ 106,469	318,164	(102)
Balance, Shares at Dec. 31, 2014	26,051,000	26,051,000
Balance at Mar. 31, 2014	$ 401,563
Net income	10,205
Balance at Jun. 30, 2014	406,439
Net income	13,746
Balance at Sep. 30, 2014	414,519
Net income	13,887
Balance at Dec. 31, 2014	$ 424,531	$ 106,469	318,164	(102)
Balance, Shares at Dec. 31, 2014	26,051,000	26,051,000
Net income	$ 6,846
Balance at Mar. 31, 2015	425,848
Balance at Dec. 31, 2014	$ 424,531	$ 106,469	318,164	(102)
Balance, Shares at Dec. 31, 2014	26,051,000	26,051,000
Net income	$ 40,470		40,470
Share-based compensation	3,399	$ 3,399
Common stock issued under stock plans, net of shares withheld for employee taxes	2,149	$ 2,149
Common stock issued under stock Plans, net of shares withheld for employee taxes, Shares		208,000
Common stock repurchased	$ (63,953)	$ (9,119)	(54,834)
Common stock repurchased, Shares	(2,407,974)	(2,408,000)
Excess tax benefit (shortfall) from equity awards	$ (292)	$ (292)
Taxes paid related to net share settlement of stock awards	(1,560)	(1,560)
Dividends accrued of $0.96, $0.98, $1.00 per share in 2013,2014 and 2015	(25,092)		(25,092)
Other comprehensive (loss) gain	35			35
Balance at Dec. 31, 2015	$ 379,687	$ 101,046	278,708	(67)
Balance, Shares at Dec. 31, 2015	23,851,000	23,851,000
Balance at Mar. 31, 2015	$ 425,848
Net income	8,490
Balance at Jun. 30, 2015	426,823
Net income	13,616
Balance at Sep. 30, 2015	389,464
Net income	11,518
Balance at Dec. 31, 2015	$ 379,687	$ 101,046	$ 278,708	$ (67)
Balance, Shares at Dec. 31, 2015	23,851,000	23,851,000