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, 2014	$ 1,228,175	$ 985,839	$ 234,498	$ 5,621	$ 2,217
Balance, shares at Dec. 31, 2014		57,437,000			9,000
Net income	72,087		72,087
Other comprehensive income	7,205			7,205
Issuance of common stock - stock option and other plans, value		$ 1,194
Issuance of common stock - stock option and other plans, shares		46,000
Issuance of common stock - restricted stock awards, net of cancelled awards, value		$ 2,934
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		277,000
Stock Repurchased and Retired During Period, Value		$ (879)
Stock Repurchased During Period, Shares		(31,000)
Dividends, Preferred Stock, Cash			(100)
Cash dividends paid on common stock	(56,480)		(56,480)
Balance, value at Sep. 30, 2015	1,254,136	$ 989,088	250,005	12,826	$ 2,217
Balance, shares at Sep. 30, 2015		57,729,000			9,000
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	74,148		74,148
Other comprehensive income	22,800			22,800
Issuance of common stock - stock option and other plans, value	1,304	$ 1,304
Issuance of common stock - stock option and other plans, shares		47,000
Issuance of common stock - restricted stock awards, net of cancelled awards, value	3,626	$ 3,626
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		310,000
Stock Repurchased and Retired During Period, Value	(1,113)	$ (1,113)
Stock Repurchased During Period, Shares		(38,000)
Dividends, Preferred Stock, Cash	(117)		117
Cash dividends paid on common stock	(66,041)		(66,041)
Balance, value at Sep. 30, 2016	$ 1,276,735	$ 994,098	$ 263,915	$ 16,505	$ 2,217
Balance, shares at Sep. 30, 2016		58,043,000			8,782