Securities - Securities with Unrealized Losses - Securities Available-for-sale (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Available-for-sale, Fair Value
Less Than 12 Months	$ 195,313	$ 185,824
12 Months or More	120,351	146,670
Total	315,664	332,494
Available-for-sale, Unrealized (Losses)
Less Than 12 Months	(5,857)	(1,623)
12 Months or More	(5,087)	(2,769)
Total	(10,944)	(4,392)
Agency mortgage-backed securities
Available-for-sale, Fair Value
Less Than 12 Months	195,313	185,824
12 Months or More	120,351	146,670
Total	315,664	332,494
Available-for-sale, Unrealized (Losses)
Less Than 12 Months	(5,857)	(1,623)
12 Months or More	(5,087)	(2,769)
Total	$ (10,944)	$ (4,392)