Consolidated Statements of Changes in Stockholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock	Paid-in Capital	Retained Earnings Substantially Restricted	Accumulated Other Comprehensive (Loss) Income
Balance at Dec. 31, 2009	$ 685,890	$ 616	$ 497,493	$ 188,129	$ (348)
Balance, shares at Dec. 31, 2009		61,619,803
Net income	42,330			42,330
Total other comprehensive income, net of tax	876				876
Total Comprehensive Income	43,206
Cash dividends declared	(37,396)			(37,396)
Public offering of stock issued	145,596	103	145,493
Public offering of stock issued, shares		10,291,465
Stock-based compensation and related taxes	850		850
Stock issuances under stock incentive plans, shares		3,805
Stock issuances under stock incentive plans, value	58		58
Balance at Dec. 31, 2010	838,204	719	643,894	193,063	528
Balance, shares at Dec. 31, 2010		71,915,073
Net income	17,471			17,471
Total other comprehensive income, net of tax	32,959				32,959
Total Comprehensive Income	50,430
Cash dividends declared	(37,395)			(37,395)
Stock-based compensation and related taxes	(1,012)		(1,012)
Balance at Dec. 31, 2011	850,227	719	642,882	173,139	33,487
Balance, shares at Dec. 31, 2011	71,915,073	71,915,073
Net income	75,516			75,516
Total other comprehensive income, net of tax	14,475				14,475
Total Comprehensive Income	89,991
Cash dividends declared	(38,124)			(38,124)
Stock-based compensation and related taxes	(1,468)		(1,468)
Stock issuances under stock incentive plans, shares		22,149
Stock issuances under stock incentive plans, value	323		323
Balance at Dec. 31, 2012	$ 900,949	$ 719	$ 641,737	$ 210,531	$ 47,962
Balance, shares at Dec. 31, 2012	71,937,222	71,937,222