Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Held to maturity, amortized cost, total	$ 207,376	$ 261,369
Fair Value
Held to maturity, fair value, total	216,000	262,213
Amortized Cost
Available for sale, amortized cost, total	1,261,879	940,765
Fair Value
Available for sale, fair value, total	1,286,858	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	2,096
Available for sale, amortized cost, due after one year through five years	10,986
Available for sale, amortized cost, due after five years through ten years	10,118
Available for sale, amortized cost, due after ten years	19,630
Available for sale, amortized cost, total	42,830
Fair Value
Available for sale, fair value, due in less than one year	2,107
Available for sale, fair value, due after one year through five years	11,612
Available for sale, fair value, due after five years through ten years	10,871
Available for sale, fair value, due after ten years	20,844
Available for sale, fair value, total	45,434
Mortgage-backed securities and collateralized mortgage obligations of U.S. government-sponsored entities
Amortized Cost
Held to maturity, amortized cost, total	207,376
Fair Value
Held to maturity, fair value, total	216,000	262,213
Amortized Cost
Available for sale, amortized cost, total	916,231	604,934
Fair Value
Available for sale, fair value, total	939,261	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	98,984	56,005
Fair Value
Available for sale, fair value, total	100,785	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	203,834	239,364
Fair Value
Available for sale, fair value, total	$ 201,378	$ 238,218