Condensed Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), net [Member]	Treasury Stock [Member]
Beginning balance at Dec. 31, 2013	$ 711,697	$ 105,563	$ 365,333	$ 334,748	$ (20,588)	$ (73,359)
Beginning balance, shares at Dec. 31, 2013		95,245,215
Net Income	36,724			36,724
Other comprehensive income (loss)	10,912				10,912
Dividends, declared (USD per share)	(19,754)			(19,754)
Discount on dividend reinvestment plan purchases	(65)		(65)
Treasury stock acquired	(30,928)					(30,928)
Treasury stock acquired, shares		(3,633,513)
Treasury stock reissued	192		35	0		157
Treasury stock reissued, shares		21,960
Restricted stock	706	$ 0	273	0		433
Restricted stock, shares		88,987
Ending balance at Sep. 30, 2014	709,484	$ 105,563	365,576	351,718	(9,676)	(103,697)
Ending balance, shares at Sep. 30, 2014		91,722,649
Beginning balance at Dec. 31, 2014	$ 716,145	$ 105,563	365,615	353,027	(4,499)	(103,561)
Beginning balance, shares at Dec. 31, 2014	91,723,028	91,723,028
Net Income	$ 40,082			40,082
Other comprehensive income (loss)	9,460				9,460
Dividends, declared (USD per share)	(18,862)			(18,862)
Treasury stock acquired	(25,383)					(25,383)
Treasury stock acquired, shares		(2,918,066)
Treasury stock reissued	192		32	0		160
Treasury stock reissued, shares		20,936
Restricted stock	1,134	$ 0	303	0		831
Restricted stock, shares		135,370
Ending balance at Sep. 30, 2015	$ 722,768	$ 105,563	$ 365,950	$ 374,247	$ 4,961	$ (127,953)
Ending balance, shares at Sep. 30, 2015	88,961,268	88,961,268