Consolidated Statements of Stockholders' Equity (Unaudited) (USD $) In Thousands, except Share data	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss), net	Total
Balance at Dec. 31, 2010	$ 122,855	$ 263,484	$ 470,828	$ (619)	$ 856,548
Balance, shares at Dec. 31, 2010	36,893,276
Net income			15,328		15,328
Other comprehensive income				2,626	2,626
Cash dividends declared ($0.24 per common share)			(8,961)		(8,961)
Common stock offering, shares	6,201,500
Common stock offering	20,651	170,267			190,918
Common stock activity, long-term incentive plan, including excess income tax benefit of $74 & $15 respectively, shares	43,831
Common stock activity, long-term incentive plan, including excess income tax benefit of $74 & $15 respectively	146	1,094			1,240
Balance at Mar. 31, 2011	143,652	434,845	477,195	2,007	1,057,699
Balance, shares at Mar. 31, 2011	43,138,607
Balance at Dec. 31, 2011	282,069	1,634,634	476,970	(26,510)	2,367,163
Balance, shares at Dec. 31, 2011	84,705,496
Net income			18,495		18,495
Other comprehensive income				6,325	6,325
Cash dividends declared ($0.24 per common share)			(20,586)		(20,586)
Common stock activity, long-term incentive plan, including excess income tax benefit of $74 & $15 respectively, shares	64,477
Common stock activity, long-term incentive plan, including excess income tax benefit of $74 & $15 respectively	215	3,591			3,806
Balance at Mar. 31, 2012	$ 282,284	$ 1,638,225	$ 474,879	$ (20,185)	$ 2,375,203
Balance, shares at Mar. 31, 2012	84,769,973