Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost
Held to maturity, amortized cost, total	$ 273,644	$ 357,949
Fair Value
Held to maturity, fair value, total	276,069	349,895
Amortized Cost
Available for sale, amortized cost, total	907,178	882,872
Fair Value
Available for sale, fair value, total	920,811	865,831
Mortgage-backed securities and collateralized mortgage obligations of U.S. government sponsored entities
Amortized Cost
Held to maturity, amortized cost, total	273,644
Fair Value
Held to maturity, fair value, total	276,069	297,099
Amortized Cost
Available for sale, amortized cost, total	562,270	567,753
Fair Value
Available for sale, fair value, total	573,846	554,006
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	21,673
Amortized Cost
Available for sale, amortized cost, total	60,809	55,569
Fair Value
Available for sale, fair value, total	62,600	$ 55,728
Collateralized loan 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	10,047
Available for sale, amortized cost, due after one year through five years	134,560
Available for sale, amortized cost, due after five years through ten years	131,057
Available for sale, amortized cost, due after ten years	8,435
Available for sale, amortized cost, total	284,099
Fair Value
Available for sale, fair value, due in less than one year	10,069
Available for sale, fair value, due after one year through five years	134,537
Available for sale, fair value, due after five years through ten years	130,712
Available for sale, fair value, due after ten years	9,047
Available for sale, fair value, total	$ 284,365