Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Number of Common Shares	Common Stock	Retained Earnings	Paid-in Capital	Accumulated Other Comprehensive Income(Loss)
Balance, shares at Dec. 31, 2013		21,893,000
Balance at Dec. 31, 2013	$ 463,419		$ 22	$ 364,515	$ 100,447	$ (1,565)
Net income	64,461			64,461
Other comprehensive (loss) income, net of tax	(1,248)					(1,248)
Proceeds from stock award exercises and issuances, shares		119,000
Proceeds from Issuance of Shares under Incentive and Share-based Compensation Plans, Including Stock Options
Proceeds from stock award exercises and issuances	160				160
Share-based compensation	3,280				3,280
Stock Repurchased During Period, Shares		(528,000)
Stock Repurchased During Period, Value	(29,483)		$ (1)		(29,482)
Excess tax benefits from exercise of stock options	1,071				1,071
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited		(4,000)
Restricted Stock Award, Forfeitures	(202)				(202)
Dividends declared	$ (38,451)			(38,451)
Balance, shares at Dec. 31, 2014	21,480,334	21,480,000
Balance at Dec. 31, 2014	$ 463,007		21	390,525	75,274	(2,813)
Net income	25,546			25,546
Other comprehensive (loss) income, net of tax	(89)					(89)
Proceeds from stock award exercises and issuances, shares		84,000
Proceeds from stock award exercises and issuances	190				190
Share-based compensation	$ 1,585				1,585
Stock Repurchased During Period, Shares	(1,555,726)	(1,556,000)
Stock Repurchased During Period, Value	$ (85,848)		(1)		(85,847)
Excess tax benefits from exercise of stock options	764				764
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited		(7,000)
Restricted Stock Award, Forfeitures	(401)				(401)
Dividends declared	$ (20,039)			(20,039)
Balance, shares at Jun. 30, 2015	20,001,272	20,001,000
Balance at Jun. 30, 2015	$ 384,715		$ 20	$ 396,032	$ (8,435)	$ (2,902)