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, 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
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 $0.98, $1.00, $1.02 per share in 2014,2015 and 2016	(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
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
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 $0.98, $1.00, $1.02 per share in 2014,2015 and 2016	(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
Net income	$ 6,566
Balance at Mar. 31, 2016	380,512
Balance at Dec. 31, 2015	$ 379,687	$ 101,046	278,708	(67)
Balance, Shares at Dec. 31, 2015	23,851,000	23,851,000
Net income	$ 38,251		38,251
Share-based compensation	3,091	$ 3,091
Common stock issued under stock plans, net of shares withheld for employee taxes	$ 37	$ 37
Common stock issued under stock Plans, net of shares withheld for employee taxes, Shares		97,000
Common stock repurchased, Shares	0
Excess tax benefit (shortfall) from equity awards	$ (1,066)	$ (1,066)
Taxes paid related to net share settlement of stock awards	(1,287)	(1,287)
Dividends accrued of $0.98, $1.00, $1.02 per share in 2014,2015 and 2016	(24,438)		(24,438)
Other comprehensive (loss) gain	12			12
Balance at Dec. 31, 2016	$ 394,287	$ 101,821	292,521	(55)
Balance, Shares at Dec. 31, 2016	23,948,000	23,948,000
Balance at Mar. 31, 2016	$ 380,512
Net income	9,079
Balance at Jun. 30, 2016	383,313
Net income	12,872
Balance at Sep. 30, 2016	390,600
Net income	9,734
Balance at Dec. 31, 2016	$ 394,287	$ 101,821	$ 292,521	$ (55)
Balance, Shares at Dec. 31, 2016	23,948,000	23,948,000