Investments - Investments by contractual maturity (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities
Within one year, amortized cost	$ 420
Within one year, estimated fair value	421
After one year through five years, amortized cost	11,062
After one year through five years, estimated fair value	12,077
After five years through ten years, amortized cost	17,552
After five years through ten years, estimated fair value	19,072
After ten years, amortized cost	77,641
After ten years, estimated fair value	84,244
Total securities with single maturity date, amortized cost	106,675
Total securities with single maturity date, estimated fair value	115,814
Debt securities, amortized cost	312,175
Available-for-sale Securities	322,931	328,413
U.S. Government agencies collateralized by residential mortgage obligations
Schedule of Available-for-sale Securities
Investment securities not due at a single maturity date, amortized cost	190,654
Investment securities not due at a single maturity date, estimated fair value	192,472
Private label residential mortgage backed securities
Schedule of Available-for-sale Securities
Investment securities not due at a single maturity date, amortized cost	7,250
Investment securities not due at a single maturity date, estimated fair value	6,669
Other equity securities
Schedule of Available-for-sale Securities
Investment securities not due at a single maturity date, amortized cost	7,596
Investment securities not due at a single maturity date, estimated fair value	$ 7,976