Investments (Details 4) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investment securities continuous unrealized loss position
Fair Value of Investments with Unrealized Losses, Less Than 12 months	$ 94,170	$ 50,561
Gross Unrealized Loss, Less Than 12 Months	2,155	1,828
Fair Value of Investments with Unrealized Losses, 12 Months or Greater	3,745	2,345
Gross Unrealized Losses, 12 Months or Greater	571	181
Fair Value of Investments with Unrealized Losses, Total	97,915	52,906
Gross Unrealized Losses, Total	2,726	2,009
Total held-to-maturity securities [Member]
Investment securities continuous unrealized loss position
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Less Than 12 Months	37,587	22,764
Held-to-Maturity, Gross Unrealized Losses, Less Than 12 Months	213	118
Held-to-Maturity, Fair Value of Investments with Unrealized Losses 12 Months or Greater	2,253	2,345
Held-to-Maturity, Gross Unrealized Losses, 12 Months or Greater	111	181
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Total	39,840	25,109
Held-to-Maturity, Gross Unrealized Losses, Total	324	299
Total held-to-maturity securities [Member] | Corporate bonds [Member]
Investment securities continuous unrealized loss position
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Less Than 12 Months	20,763	10,734
Held-to-Maturity, Gross Unrealized Losses, Less Than 12 Months	20	12
Held-to-Maturity, Fair Value of Investments with Unrealized Losses 12 Months or Greater
Held-to-Maturity, Gross Unrealized Losses, 12 Months or Greater
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Total	20,763	10,734
Held-to-Maturity, Gross Unrealized Losses, Total	20	12
Total held-to-maturity securities [Member] | States and political subdivisions [Member]
Investment securities continuous unrealized loss position
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Less Than 12 Months	16,824	11,913
Held-to-Maturity, Gross Unrealized Losses, Less Than 12 Months	193	106
Held-to-Maturity, Fair Value of Investments with Unrealized Losses 12 Months or Greater
Held-to-Maturity, Gross Unrealized Losses, 12 Months or Greater
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Total	16,824	11,913
Held-to-Maturity, Gross Unrealized Losses, Total	193	106
Total held-to-maturity securities [Member] | U.S. agency-based mortgage-backed securities [Member]
Investment securities continuous unrealized loss position
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Less Than 12 Months		117
Held-to-Maturity, Fair Value of Investments with Unrealized Losses 12 Months or Greater		68
Held-to-Maturity, Gross Unrealized Losses, 12 Months or Greater		5
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Total		185
Held-to-Maturity, Gross Unrealized Losses, Total		5
Total held-to-maturity securities [Member] | Asset-backed securities [Member]
Investment securities continuous unrealized loss position
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Less Than 12 Months
Held-to-Maturity, Gross Unrealized Losses, Less Than 12 Months
Held-to-Maturity, Fair Value of Investments with Unrealized Losses 12 Months or Greater	2,243	2,277
Held-to-Maturity, Gross Unrealized Losses, 12 Months or Greater	111	176
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Total	2,243	2,277
Held-to-Maturity, Gross Unrealized Losses, Total	111	176
Total available-for-sale securities [Member]
Investment securities continuous unrealized loss position
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	56,583	27,797
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	1,942	1,710
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	58,075	27,797
Available-for Sale, Gross Unrealized Losses, Total	2,402	1,710
Fair Value of Investments with Unrealized Losses, 12 Months or Greater	1,492
Gross Unrealized Losses, 12 Months or Greater	460
Total available-for-sale securities [Member] | Corporate bonds [Member]
Investment securities continuous unrealized loss position
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	11,381	6,411
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	12	24
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	11,381	6,411
Available-for Sale, Gross Unrealized Losses, Total	12	24
Fair Value of Investments with Unrealized Losses, 12 Months or Greater
Gross Unrealized Losses, 12 Months or Greater
Total available-for-sale securities [Member] | States and political subdivisions [Member]
Investment securities continuous unrealized loss position
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	31,529	6,281
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	444	142
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	31,529	6,281
Available-for Sale, Gross Unrealized Losses, Total	444	142
Fair Value of Investments with Unrealized Losses, 12 Months or Greater
Gross Unrealized Losses, 12 Months or Greater
Total available-for-sale securities [Member] | U.S. agency-based mortgage-backed securities [Member]
Investment securities continuous unrealized loss position
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	8,731	10,919
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	1,046	859
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	8,731	10,919
Available-for Sale, Gross Unrealized Losses, Total	1,046	859
Fair Value of Investments with Unrealized Losses, 12 Months or Greater
Gross Unrealized Losses, 12 Months or Greater
Total available-for-sale securities [Member] | Equity Securities [Member]
Investment securities continuous unrealized loss position
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	4,942	4,186
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	440	685
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	6,434	4,186
Available-for Sale, Gross Unrealized Losses, Total	900	685
Fair Value of Investments with Unrealized Losses, 12 Months or Greater	1,492
Gross Unrealized Losses, 12 Months or Greater	$ 460