Consolidated Statements of Changes In Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Balance Beginning at Dec. 31, 2013	$ 1,001,442	$ 858	$ 414,293	$ 853,740	$ (26,792)	$ (240,657)
Balance Beginning (in Shares) at Dec. 31, 2013		75,071
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	62,653			54,713	7,940
Common dividends declared ($0.23 and $0.27 per common share)	(17,324)			(17,324)
Share-based compensation expense	4,461		4,461
Restricted stock activity	(1,895)		(9,833)			7,938
Restricted stock activity (in Shares)		215
Treasury stock issued to benefit plans	339		(132)			471
Treasury stock issued to benefit plans (in Shares)		(9)
Balance Ending at Sep. 30, 2014	1,049,676	$ 858	408,789	891,129	(18,852)	(232,248)
Balance Ending (in Shares) at Sep. 30, 2014		75,295
Balance Beginning at Dec. 31, 2014	$ 1,100,775	$ 882	449,798	899,516	(15,855)	(233,566)
Balance Beginning (in Shares) at Dec. 31, 2014	77,695	77,695
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	$ 65,777			65,740	37
Common dividends declared ($0.23 and $0.27 per common share)	(21,047)			(21,047)
Purchase of treasury stock (in Shares)		(7)
Purchase of treasury stock	(120)					(120)
Share-based compensation expense	12,223		5,459			6,764
Restricted stock activity	(10,108)		(10,108)			0
Restricted stock activity (in Shares)		255
Treasury stock issued to benefit plans	169		(112)			281
Treasury stock issued to benefit plans (in Shares)		(1)
Balance Ending at Sep. 30, 2015	$ 1,147,669	$ 882	$ 445,037	$ 944,209	$ (15,818)	$ (226,641)
Balance Ending (in Shares) at Sep. 30, 2015	77,942	77,942