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]
Cumulative effect of adoption of ASU 2018-02 | Effect of ASU Adoption [Member]	$ 0				$ 0
Beginning balance at Dec. 31, 2016	749,929	$ 105,563	$ 366,426	$ 412,764	(7,027)	$ (127,797)
Beginning balance, shares at Dec. 31, 2016		89,007,077
Net Income	15,888			15,888
Other comprehensive income (loss)	944				944
Dividends, declared (USD per share)	(7,119)			(7,119)
Treasury stock acquired	(1,102)					(1,102)
Treasury stock acquired, shares		(78,632)
Stock Issued During Period, Value, Treasury Stock Reissued	2,258		1,044	0		1,214
Stock Issued During Period, Shares, Treasury Stock Reissued		158,638
Restricted stock	197	$ 0	137	0		60
Restricted stock, shares		26,000
Stock Issued During Period, Value, Treasury Stock Reissued	2,258
Ending balance at Mar. 31, 2017	760,995	$ 105,563	367,607	421,533	(6,083)	(127,625)
Ending balance, shares at Mar. 31, 2017		89,113,083
Cumulative effect of adoption of ASU 2018-02 | Effect of ASU Adoption [Member]	0			1,344	(1,344)
Beginning balance (Scenario, Previously Reported [Member]) at Dec. 31, 2017	888,127	$ 113,915	470,123	437,416	(6,173)	(127,154)
Beginning balance at Dec. 31, 2017	$ 888,127	$ 113,915	470,123	438,760	(7,517)	(127,154)
Beginning balance, shares (Scenario, Previously Reported [Member]) at Dec. 31, 2017		97,456,478
Beginning balance, shares at Dec. 31, 2017	97,456,478	97,456,478
Net Income	$ 23,270			23,270
Other comprehensive income (loss)	(5,492)				(5,492)
Dividends, declared (USD per share)	(7,803)			(7,803)
Treasury stock acquired	(1,079)					(1,079)
Treasury stock acquired, shares		(72,307)
Stock Issued During Period, Value, Treasury Stock Reissued	2,257		1,108	0		1,149
Stock Issued During Period, Shares, Treasury Stock Reissued		149,480
Restricted stock	69	$ 0	537	0		(468)
Restricted stock, shares		69,500
Stock Issued During Period, Value, Treasury Stock Reissued	2,257
Ending balance at Mar. 31, 2018	$ 899,349	$ 113,915	$ 471,768	$ 454,227	$ (13,009)	$ (127,552)
Ending balance, shares at Mar. 31, 2018	97,603,151	97,603,151