Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Preferred Stock [Member]
Balance, value at Dec. 31, 2015	$ 1,242,128	$ 990,281	$ 255,925	$ (6,295)	$ 2,217
Balance, shares at Dec. 31, 2015		57,724,000			9,000
Net income	21,259		21,259
Other comprehensive income	18,638			18,638
Issuance of common stock - stock option and other plans, value		$ 598
Issuance of common stock - stock option and other plans, shares		20,000
Issuance of common stock - restricted stock awards, net of cancelled awards, value		$ 1,180
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		299,000
Stock Repurchased and Retired During Period, Value		$ (1,033)
Stock Repurchased During Period, Shares		(35,000)
Dividends, Preferred Stock, Cash			(39)
Cash dividends paid on common stock	(21,943)		(21,943)
Balance, value at Mar. 31, 2016	1,260,788	$ 991,026	255,202	12,343	$ 2,217
Balance, shares at Mar. 31, 2016		58,008,000			9,000
Cumulative Effect of New Accounting Principle in Period of Adoption	67	$ 184	(117)
Balance, value at Dec. 31, 2016	1,251,012	$ 995,837	271,957	(18,999)	$ 2,217
Balance, shares at Dec. 31, 2016		58,042,000			8,782
Net income	29,199		29,199
Other comprehensive income	6,393			6,393
Issuance of common stock - stock option and other plans, value	1,145	$ 1,145
Issuance of common stock - stock option and other plans, shares		28,000
Issuance of common stock - restricted stock awards, net of cancelled awards, value	2,358	$ 2,358
Conversion of Stock, Shares Converted					(9,000)
Conversion of Stock, Amount Converted					$ (2,217)
Conversion of Stock, New Issuance		102,000
Conversion of Stock, Amount Issued	0	$ 2,217
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		207,000
Stock Repurchased and Retired During Period, Value	(2,039)	$ (2,039)
Stock Repurchased During Period, Shares		(50,000)
Cash dividends paid on common stock	(12,792)		(12,792)
Balance, value at Mar. 31, 2017	$ 1,275,343	$ 999,702	$ 288,247	$ (12,606)	$ 0
Balance, shares at Mar. 31, 2017		58,329,000			0