Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($)	Shares Purchased to Fund Options Exercised [Member] Treasury Stock [Member]	Shares Purchased to Fund Options Exercised [Member]	Restricted Stock Awards Repurchased to Satisfy Tax Obligations [Member] Treasury Stock [Member]	Restricted Stock Awards Repurchased to Satisfy Tax Obligations [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	AOCI Attributable to Parent [Member]	Total
Balance at Dec. 31, 2014					$ 315,000	$ 206,437,000	$ 289,623,000	$ (37,221,000)	$ (2,907,000)	$ 456,247,000
Net Income							23,567,000			23,567,000
Award of common shares released from Employee Benefit Trust						1,969,000				1,969,000
Vesting of restricted stock unit award						(3,074,000)	(503,000)	3,577,000
Exercise of stock options						(4,000)	(8,000)	154,000		142,000
Stock-based compensation expense						3,549,000				3,549,000
Stock-based income tax benefit						380,000				380,000
Purchase of treasury shares	$ (12,380,000)	$ (12,380,000)	$ (1,110,000)	$ (1,110,000)
Dividends on common stock							(9,379,000)			(9,379,000)
Other comprehensive income									(849,000)	(849,000)
Balance at Jun. 30, 2015					315,000	209,257,000	303,300,000	(46,980,000)	(3,756,000)	462,136,000
Balance at Dec. 31, 2015					315,000	210,652,000	316,530,000	(48,868,000)	(5,562,000)	473,067,000
Net Income							39,996,000			39,996,000
Award of common shares released from Employee Benefit Trust						1,912,000				1,912,000
Vesting of restricted stock unit award						(4,047,000)	(396,000)	4,443,000
Exercise of stock options						2,000		159,000		127,000
Stock-based compensation expense						3,673,000				3,673,000
Stock-based income tax benefit						421,000				421,000
Purchase of treasury shares	$ (7,492,000)	$ (7,492,000)	$ (1,593,000)	$ (1,593,000)
Dividends on common stock							(9,878,000)			(9,878,000)
Other comprehensive income									8,650,000	8,650,000
Balance at Jun. 30, 2016					$ 315,000	$ 212,613,000	$ 346,218,000	$ (53,351,000)	$ 3,088,000	$ 508,883,000