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	46,307		46,307
Other comprehensive income	(2,832)			(2,832)
Issuance of common stock - stock option and other plans, value		$ 519
Issuance of common stock - stock option and other plans, shares		21,000
Issuance of common stock - restricted stock awards, net of cancelled awards, value		$ 1,836
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		282,000
Stock Repurchased and Retired During Period, Value		$ (874)
Stock Repurchased During Period, Shares		(31,000)
Dividends, Preferred Stock, Cash			(66)
Cash dividends paid on common stock	(36,851)		(36,851)
Balance, value at Jun. 30, 2015	1,236,214	$ 987,320	243,888	2,789	$ 2,217
Balance, shares at Jun. 30, 2015		57,709,000			9,000
Stock Issued During Period, Shares, New Issues					0
Stock Issued During Period, Value, New Issues					$ 0
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	46,664		46,664
Other comprehensive income	27,106			27,106
Issuance of common stock - stock option and other plans, value	603	$ 603
Issuance of common stock - stock option and other plans, shares		21,000
Issuance of common stock - restricted stock awards, net of cancelled awards, value	2,551	$ 2,551
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		317,000
Stock Repurchased and Retired During Period, Value	(1,092)	$ (1,092)
Stock Repurchased During Period, Shares		(37,000)
Dividends, Preferred Stock, Cash	(77)		77
Cash dividends paid on common stock	(43,404)		(43,404)
Balance, value at Jun. 30, 2016	$ 1,274,479	$ 992,343	$ 259,108	$ 20,811	$ 2,217
Balance, shares at Jun. 30, 2016		58,025,000			8,782