Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Balance, value at Dec. 31, 2012	$ 764,008	$ 0	$ 581,471	$ 162,388	$ 20,149
Balance (in shares) at Dec. 31, 2012		0	39,686,000
Net income	60,016			60,016
Other comprehensive income	(32,193)				(32,193)
Issuance of common stock, net of offering costs, shares		9,000	11,380,000
Issuance of common stock, net of offering costs, value	276,181	$ 2,217	$ 273,964
Stock Adjustment Value Deferred Compensation	517
Issuance of common stock - stock option and other plans, shares			73,000
Issuance of common stock - stock option and other plans, value	1,243		$ 1,243
Issuance of common stock - restricted stock awards, net of canceled awards, shares			144,000
Issuance of common stock - restricted stock awards, net of canceled awards, value	2,693		$ 2,693
Tax benefit deficiency associated with share-based compensation			$ 1,103
Purchase and retirement of common stock (in shares)			(18,000)
Purchase and retirement of common stock, value	(429)		$ (429)
Dividends, Preferred Stock				0
Dividends, Preferred Stock, Cash	(32)
Cash dividends paid on common stock	(19,858)			(19,858)
Balance, value at Dec. 31, 2013	$ 1,053,249	$ 2,217	$ 860,562	202,514	(12,044)
Balance (in shares) at Dec. 31, 2013		9,000	51,265,000
Preferred Stock, Dividends, Per Share, Cash Paid	$ 0.31
Common Stock, Dividends, Per Share, Cash Paid	$ 0.41
Net income	$ 81,574			81,574
Other comprehensive income	17,665				17,665
Issuance of common stock, net of offering costs, shares		0	4,208,000
Issuance of common stock, net of offering costs, value	116,907	$ 0	$ 116,907
Stock Issued During Period, Shares, Conversion of Warrants			1,722,000
Stock Issued During Period, Value, Conversion of Warrants			$ 5,000
Stock Adjustment Value Deferred Compensation	(1)
Issuance of common stock - stock option and other plans, shares			41,000
Issuance of common stock - stock option and other plans, value	929		$ 929
Issuance of common stock - restricted stock awards, net of canceled awards, shares			225,000
Issuance of common stock - restricted stock awards, net of canceled awards, value	2,859		$ 2,859
Tax benefit deficiency associated with share-based compensation	205		$ 205
Purchase and retirement of common stock (in shares)			(24,000)
Purchase and retirement of common stock, value	(622)		$ (622)
Dividends, Preferred Stock, Cash	(96)
Cash dividends paid on common stock	(49,494)			(49,494)
Balance, value at Dec. 31, 2014	$ 1,228,175	$ 2,217	$ 985,839	234,498	5,621
Balance (in shares) at Dec. 31, 2014		9,000	57,437,000
Preferred Stock, Dividends, Per Share, Cash Paid	$ 0.94
Common Stock, Dividends, Per Share, Cash Paid	$ 0.94
Net income	$ 98,827			98,827
Other comprehensive income	$ (11,916)				(11,916)
Issuance of common stock - stock option and other plans, shares	7,898		49,000
Issuance of common stock - stock option and other plans, value	$ 1,258		$ 1,258
Issuance of common stock - restricted stock awards, net of canceled awards, shares			270,000
Issuance of common stock - restricted stock awards, net of canceled awards, value	4,090		$ 4,090
Purchase and retirement of common stock (in shares)			(32,000)
Purchase and retirement of common stock, value	(906)		$ (906)
Dividends, Preferred Stock, Cash	(137)
Cash dividends paid on common stock	(77,263)			(77,263)
Balance, value at Dec. 31, 2015	$ 1,242,128	$ 2,217	$ 990,281	$ 255,925	$ (6,295)
Balance (in shares) at Dec. 31, 2015		9,000	57,724,000
Preferred Stock, Dividends, Per Share, Cash Paid	$ 1.34
Common Stock, Dividends, Per Share, Cash Paid	$ 1.34