Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Held to maturity, amortized cost, total	$ 252,373	$ 261,369
Fair Value
Held to maturity, fair value, total	261,218	262,213
Amortized Cost
Available for sale, amortized cost, total	904,022	940,765
Fair Value
Available for sale, fair value, total	910,311	946,855
Other Debt Obligations
Amortized Cost
Held to maturity, amortized cost, due in less than one year	0
Held to maturity, amortized cost, due after one year through five years	0
Held to maturity, amortized cost, due after five years through ten years	0
Held to maturity, amortized cost, due after ten years	0
Held to maturity, amortized cost, total	0
Fair Value
Held to maturity, fair value, due in less than one year	0
Held to maturity, fair value, due after one year through five years	0
Held to maturity, fair value, due after five years through ten years	0
Held to maturity, fair value, due after ten years	0
Held to maturity, fair value, total	0
Amortized Cost
Available for sale, amortized cost, due in less than one year	2,068
Available for sale, amortized cost, due after one year through five years	8,374
Available for sale, amortized cost, due after five years through ten years	9,040
Available for sale, amortized cost, due after ten years	17,723
Available for sale, amortized cost, total	37,205
Fair Value
Available for sale, fair value, due in less than one year	2,091
Available for sale, fair value, due after one year through five years	8,585
Available for sale, fair value, due after five years through ten years	9,546
Available for sale, fair value, due after ten years	18,572
Available for sale, fair value, total	38,794
Mortgage-backed securities and collateralized mortgage obligations of U.S. government sponsored entities
Amortized Cost
Held to maturity, amortized cost, total	252,373
Fair Value
Held to maturity, fair value, total	261,218	262,213
Amortized Cost
Available for sale, amortized cost, total	608,711	604,934
Fair Value
Available for sale, fair value, total	635,219	609,207
Private mortgage-backed securities and collateralized mortgage obligations
Amortized Cost
Held to maturity, amortized cost, total	0
Fair Value
Held to maturity, fair value, total	0
Amortized Cost
Available for sale, amortized cost, total	52,868	56,005
Fair Value
Available for sale, fair value, total	50,569	57,561
Collateralized loan obligations
Amortized Cost
Held to maturity, amortized cost, total	0
Fair Value
Held to maturity, fair value, total	0
Amortized Cost
Available for sale, amortized cost, total	205,238	239,364
Fair Value
Available for sale, fair value, total	$ 185,729	$ 238,218