Consolidated Statements of Financial Position (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Held-to-maturity, fair value	$ 272,407	$ 268,271	$ 261,405
Accumulated depreciation of premises and equipment	$ 102,163	$ 100,261	$ 94,068
Preferred stock, no par value
Preferred stock, shares authorized	200,000	200,000	200,000
Preferred stock, shares issued	0	0	0
Common stock, par value	$ 1	$ 1	$ 1
Common stock, shares authorized	45,000,000	45,000,000	45,000,000
Common stock, shares issued	29,865,841	29,789,825	27,532,377
Common stock, shares outstanding	29,865,841	29,789,825	27,532,377