Securities (Details 2) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($) item	Dec. 31, 2014 USD ($) item
Securities
Available for sale, fair value	$ 902,766	$ 759,065
Held to maturity, fair value	$ 50,288	$ 2,425
General obligation bonds
Securities
Number of issuers | item	255	187
Amortized Cost	$ 206,247	$ 183,670
Fair Value	809	982
Average Exposure Per Issuer (Fair Value)	203,346	$ 181,596
Amount of largest exposure to a single issuer	$ 3,400
Percentage of the entity's stockholders equity in excess of aggregate book or market value	10.00%	10.00%
Percentage of underlying asset rated by at least a specified nationally recognized statistical rating organization	97.50%	97.10%
Minimum number of nationally recognized statistical rating organizations | item	1	1
Percentage of underlying asset unrated	2.50%	2.90%
General obligation bonds | Illinois
Securities
Number of issuers | item	88	63
Amortized Cost	$ 73,122	$ 61,058
Fair Value	831	969
Average Exposure Per Issuer (Fair Value)	$ 71,965	$ 59,979
General obligation bonds | Wisconsin
Securities
Number of issuers | item	38	39
Amortized Cost	$ 33,304	$ 36,365
Fair Value	876	932
Average Exposure Per Issuer (Fair Value)	$ 32,955	$ 36,165
General obligation bonds | Michigan
Securities
Number of issuers | item	39	33
Amortized Cost	$ 29,600	$ 30,739
Fair Value	759	931
Average Exposure Per Issuer (Fair Value)	$ 29,111	$ 30,400
General obligation bonds | Pennsylvania
Securities
Number of issuers | item	10	10
Amortized Cost	$ 12,908	$ 12,761
Fair Value	1,291	1,276
Average Exposure Per Issuer (Fair Value)	$ 12,815	$ 12,756
General obligation bonds | Ohio
Securities
Number of issuers | item	10	8
Amortized Cost	$ 11,055	$ 9,922
Fair Value	1,105	1,240
Average Exposure Per Issuer (Fair Value)	$ 10,995	$ 9,954
General obligation bonds | Texas
Securities
Number of issuers | item	18	7
Amortized Cost	$ 12,279	$ 7,313
Fair Value	682	1,045
Average Exposure Per Issuer (Fair Value)	$ 12,179	$ 7,364
General obligation bonds | Iowa
Securities
Number of issuers | item	3	3
Amortized Cost	$ 5,617	$ 6,142
Fair Value	1,872	2,047
Average Exposure Per Issuer (Fair Value)	$ 5,551	$ 6,116
General obligation bonds | Other
Securities
Number of issuers | item	49	24
Amortized Cost	$ 28,362	$ 19,370
Fair Value	579	807
Average Exposure Per Issuer (Fair Value)	$ 27,775	$ 18,862
Revenue bonds
Securities
Number of issuers | item	37	33
Amortized Cost	$ 35,588	$ 37,862
Fair Value	962	1,147
Average Exposure Per Issuer (Fair Value)	35,417	38,013
Amount of largest exposure to a single issuer	$ 3,000	$ 3,000
Percentage of the entity's stockholders equity in excess of aggregate book or market value	10.00%	10.00%
Minimum number of nationally recognized statistical rating organizations | item	1	1
Revenue bonds | Illinois
Securities
Number of issuers | item	7	4
Amortized Cost	$ 8,925	$ 6,708
Fair Value	1,275	1,677
Average Exposure Per Issuer (Fair Value)	$ 8,908	$ 6,772
Revenue bonds | Indiana
Securities
Number of issuers | item	9	8
Amortized Cost	$ 10,255	$ 12,469
Fair Value	1,139	1,559
Average Exposure Per Issuer (Fair Value)	$ 10,194	$ 12,520
Revenue bonds | Other
Securities
Number of issuers | item	21	21
Amortized Cost	$ 16,408	$ 18,685
Fair Value	781	890
Average Exposure Per Issuer (Fair Value)	16,315	18,721
Obligations of states and political subdivisions
Securities
Available for sale, fair value	192,597	220,161
Held to maturity, fair value	$ 49,238	$ 1,371
Number of issuers | item	292	220
Total Risk Based Capital for rated securities (as a percent)	100.00%
Total Risk Based Capital for unrated securities (as a percent)	15.00%
Obligations of states and political subdivisions | General obligation bonds
Securities
Fair Value	$ 206,200	$ 183,700
Number of states in which investment is held | item	30	23
Number of states in which investment is held in excess of aggregate fair value | item	7	7
Aggregate fair value	$ 5,000	$ 5,000
Obligations of states and political subdivisions | Revenue bonds
Securities
Fair Value	$ 35,600	$ 37,900
Number of states in which investment is held | item	17	15
Number of states in which investment is held in excess of aggregate fair value | item	2	2
Aggregate fair value	$ 5,000	$ 5,000