Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized Cost
Held to maturity, amortized cost, total	$ 512,307	$ 184,484
Fair Value
Held to maturity, fair value, total	500,720	192,179
Amortized Cost
Available for sale, amortized cost, total	1,039,557	1,371,539
Fair Value
Available for sale, fair value, total	1,051,396	1,398,157
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	435
Available for sale, amortized cost, due after one year through five years	12,400
Available for sale, amortized cost, due after five years through ten years	8,113
Available for sale, amortized cost, due after ten years	19,652
Available for sale, amortized cost, total	40,600
Fair Value
Available for sale, fair value, due in less than one year	437
Available for sale, fair value, due after one year through five years	13,310
Available for sale, fair value, due after five years through ten years	8,464
Available for sale, fair value, due after ten years	20,611
Available for sale, fair value, total	42,822
Mortgage-backed securities and collateralized mortgage obligations of U.S. government-sponsored entities
Amortized Cost
Held to maturity, amortized cost, total	512,307
Fair Value
Held to maturity, fair value, total	500,720	192,179
Amortized Cost
Available for sale, amortized cost, total	746,409	1,038,437
Fair Value
Available for sale, fair value, total	754,219	1,060,654
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	80,156	89,284
Fair Value
Available for sale, fair value, total	81,884	91,205
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	172,392	202,563
Fair Value
Available for sale, fair value, total	$ 172,471	$ 202,195