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, 2013	$ 1,053,249	$ 2,217	$ 860,562	$ 202,514	$ (12,044)
Balance (in shares) at Dec. 31, 2013		9,000	51,265,000
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
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			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
Net income	$ 104,866			104,866
Other comprehensive income	(12,704)				(12,704)
Stock Adjustment Value Deferred Compensation	$ (11)
Issuance of common stock - stock option and other plans, shares	8,558		50,000
Issuance of common stock - stock option and other plans, value	$ 1,349		$ 1,349
Issuance of common stock - restricted stock awards, net of canceled awards, shares			306,000
Issuance of common stock - restricted stock awards, net of canceled awards, value	5,009		$ 5,009
Tax benefit deficiency associated with share-based compensation	334		$ 334
Purchase and retirement of common stock (in shares)			(38,000)
Purchase and retirement of common stock, value	(1,125)		$ (1,125)
Dividends, Preferred Stock, Cash	(157)
Cash dividends paid on common stock	(88,677)			(88,677)
Balance, value at Dec. 31, 2016	$ 1,251,012	$ 2,217	$ 995,837	$ 271,957	$ (18,999)
Balance (in shares) at Dec. 31, 2016		9,000	58,042,000
Preferred Stock, Dividends, Per Share, Cash Paid	$ 1.53
Common Stock, Dividends, Per Share, Cash Paid	$ 1.53