Securities (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Gain on sale of investments	$ 0	$ (2)
Gross unrealized losses	17,855		$ 9,535
Cumulative OTTI charges	7,132	$ 7,132	7,132	$ 13,974
Amortized Cost	812,002		811,369
Securities available-for-sale	$ 805,558		$ 814,931
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Basis point spread on variable rate	1.60%
Minimum [Member] | Standard Poors [Member]
Schedule of Available-for-sale Securities [Line Items]
Credit Quality Indicator Pricing	73.69
Minimum [Member] | Moody Investor Service [Member]
Schedule of Available-for-sale Securities [Line Items]
Credit Quality Indicator Pricing	20.96
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Basis point spread on variable rate	1.80%
Maximum [Member] | Standard Poors [Member]
Schedule of Available-for-sale Securities [Line Items]
Credit Quality Indicator Pricing	83.88
Maximum [Member] | Moody Investor Service [Member]
Schedule of Available-for-sale Securities [Line Items]
Credit Quality Indicator Pricing	49.56