Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets:
Securities available-for-sale at fair value (amortized cost)	$ 598,878	$ 511,731
Securities held-to-maturity at amortized cost (fair value)	1,664	1,661
Core deposit intangible (accumulated amortization)	$ 7,659	$ 7,499
Shareholders' equity:
Preferred stock, shares authorized (in shares)	300,000	300,000
Preferred stock, shares unissued (in shares)	300,000	300,000
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	25,000,000	25,000,000
Common stock, shares outstanding (in shares)	15,604,383	15,429,992