Securities (Details 2) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015 item	Dec. 31, 2014 item
Securities
Available for sale, fair value	$ 831,614,000	$ 759,065,000
Held to maturity, fair value	35,387,000	2,425,000
General obligation bonds
Securities
Number of issuers	255	187
Amortized Cost	204,045,000	183,670,000
Fair Value	800,000	982,000
Average Exposure Per Issuer (Fair Value)	200,882,000	181,596,000
Amount of largest exposure to a single issuer	3,400,000
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	98.10%	97.10%
Minimum number of nationally recognized statistical rating organizations	1	1
Percentage of underlying asset unrated	1.90%	2.90%
General obligation bonds | Illinois
Securities
Number of issuers	84	63
Amortized Cost	66,809,000	61,058,000
Fair Value	795,000	969,000
Average Exposure Per Issuer (Fair Value)	65,460,000	59,979,000
General obligation bonds | Wisconsin
Securities
Number of issuers	37	39
Amortized Cost	31,180,000	36,365,000
Fair Value	843,000	932,000
Average Exposure Per Issuer (Fair Value)	30,840,000	36,165,000
General obligation bonds | Michigan
Securities
Number of issuers	41	33
Amortized Cost	33,570,000	30,739,000
Fair Value	819,000	931,000
Average Exposure Per Issuer (Fair Value)	33,041,000	30,400,000
General obligation bonds | Pennsylvania
Securities
Number of issuers	11	10
Amortized Cost	13,226,000	12,761,000
Fair Value	1,202,000	1,276,000
Average Exposure Per Issuer (Fair Value)	13,149,000	12,756,000
General obligation bonds | Ohio
Securities
Number of issuers	10	8
Amortized Cost	11,084,000	9,922,000
Fair Value	1,108,000	1,240,000
Average Exposure Per Issuer (Fair Value)	11,038,000	9,954,000
General obligation bonds | Texas
Securities
Number of issuers	18	7
Amortized Cost	12,376,000	7,313,000
Fair Value	688,000	1,045,000
Average Exposure Per Issuer (Fair Value)	12,299,000	7,364,000
General obligation bonds | Iowa
Securities
Number of issuers	3	3
Amortized Cost	6,191,000	6,142,000
Fair Value	2,063,000	2,047,000
Average Exposure Per Issuer (Fair Value)	6,113,000	6,116,000
General obligation bonds | Other
Securities
Number of issuers	51	24
Amortized Cost	29,609,000	19,370,000
Fair Value	581,000	807,000
Average Exposure Per Issuer (Fair Value)	28,942,000	18,862,000
Revenue bonds
Securities
Number of issuers	40	33
Amortized Cost	39,357,000	37,862,000
Fair Value	984,000	1,147,000
Average Exposure Per Issuer (Fair Value)	39,257,000	38,013,000
Amount of largest exposure to a single issuer	3,000,000	3,000,000
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	1	1
Revenue bonds | Illinois
Securities
Number of issuers	6	4
Amortized Cost	7,710,000	6,708,000
Fair Value	1,285,000	1,677,000
Average Exposure Per Issuer (Fair Value)	7,708,000	6,772,000
Revenue bonds | Indiana
Securities
Number of issuers	11	8
Amortized Cost	12,666,000	12,469,000
Fair Value	1,151,000	1,559,000
Average Exposure Per Issuer (Fair Value)	12,616,000	12,520,000
Revenue bonds | Other
Securities
Number of issuers	23	21
Amortized Cost	18,981,000	18,685,000
Fair Value	825,000	890,000
Average Exposure Per Issuer (Fair Value)	18,933,000	18,721,000
Obligations of states and political subdivisions
Securities
Available for sale, fair value	209,081,000	220,161,000
Held to maturity, fair value	34,321,000	1,371,000
Number of issuers	295	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	204,000,000	183,700,000
Number of states in which investment is held	30	23
Number of states in which investment is held in excess of aggregate fair value	7	7
Aggregate fair value	5,000,000	5,000,000
Obligations of states and political subdivisions | Revenue bonds
Securities
Fair Value	39,400,000	37,900,000
Number of states in which investment is held	17	15
Number of states in which investment is held in excess of aggregate fair value	2	2
Aggregate fair value	$ 5,000,000	$ 5,000,000