Investment Securities Available-for-Sale (Details 2) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Amortized cost	$ 590,371	$ 594,386
Estimated fair value	578,317	589,268
US Agency Securities [Member]
One year or less, amortized cost	111,940	109,893
One year or less, estimated fair value	108,886	108,198
After one year through five years, amortized cost	70,523	74,106
After one year through five years, estimated fair value	69,917	73,916
Five years through ten years, amortized cost	13,747	14,116
Five years through ten years, estimated fair value	13,288	13,870
Residential Mortgage Backed Securities [Member]
Amortized cost, without maturity date	337,362	322,067
Estimated fair value, without maturity date	329,240	317,836
Municipal Bonds [Member]
One year or less, amortized cost	5,078	5,068
One year or less, estimated fair value	5,139	5,171
After one year through five years, amortized cost	19,366	19,405
After one year through five years, estimated fair value	19,654	19,879
Five years through ten years, amortized cost	23,064	35,432
Five years through ten years, estimated fair value	22,686	35,846
After ten years, amortized cost	1,069	1,071
After ten years, estimated fair value	1,126	1,161
Corporate Bonds [Member]
After one year through five years, amortized cost	6,504	11,510
After one year through five years, estimated fair value	6,663	11,673
After ten years, amortized cost	1,500	1,500
After ten years, estimated fair value	1,500	1,500
Investment Securities [Member]
Amortized cost, without maturity date	218	218
Estimated fair value, without maturity date	$ 218	$ 218