Securities - Contractural Maturities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2019	Dec. 31, 2018
Securities Available-for-Sale, Amortized Cost
Due in one year or less	$ 11,629
Due after one year through five years	6,814
Due after five years through ten years	6,189
Due after ten years	266,349
Debt securities excluding securities not due at a single maturity date	290,981
Total	$ 505,544	$ 505,544	$ 546,867
Securities Available-for-Sale, Weighted Average Yield
Due in one year or less (as a percent)	2.69%
Due after one year through five years (as a percent)	2.53%
Due after five years through ten years (as a percent)	3.50%
Due after ten years (as a percent)	3.05%
Debt securities (as a percent)	3.03%
Total (as a percent)	3.40%
Securities Available-for-Sale, Fair Value
Due in one year or less	$ 11,643
Due after one year through five years	6,818
Due after five years through ten years	6,410
Due after ten years	270,621
Debt securities	295,492
Fair Value	509,090	509,090	541,248
Collateralized Mortgage Obligations [Member]
Securities Available-for-Sale, Amortized Cost
Total		65,354	66,494
Securities Available-for-Sale, Fair Value
Fair Value		64,330	64,429
Asset-backed Securities [Member]
Securities Available-for-Sale, Amortized Cost
Securities not due at a single maturity date	$ 70,123
Total		70,123	108,574
Securities Available-for-Sale, Weighted Average Yield
Securities not due at a single maturity date, Weighted Average Yield (as a percent)	3.71%
Securities Available-for-Sale, Fair Value
Securities not due at a single maturity date	$ 70,811
Fair Value		70,811	109,514
Collateralized loan obligations
Securities Available-for-Sale, Amortized Cost
Securities not due at a single maturity date	$ 63,808
Total		63,808	65,162
Securities Available-for-Sale, Weighted Average Yield
Securities not due at a single maturity date, Weighted Average Yield (as a percent)	4.96%
Securities Available-for-Sale, Fair Value
Securities not due at a single maturity date	$ 63,151
Fair Value		$ 63,151	$ 64,289
Mortgage-backed and collateralized mortgage obligations
Securities Available-for-Sale, Amortized Cost
Securities not due at a single maturity date	$ 80,632
Securities Available-for-Sale, Weighted Average Yield
Securities not due at a single maturity date, Weighted Average Yield (as a percent)	3.26%
Securities Available-for-Sale, Fair Value
Securities not due at a single maturity date	$ 79,636