Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets:
Securities available-for-sale, at amortized cost	$ 511,731	$ 332,658
Securities held-to-maturity, at fair value	1,661	1,662
Core deposit intangible, accumulated amortization	$ 7,499	$ 7,260
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)	15,429,992	15,334,410