Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Amortized Cost
Held to maturity, amortized cost, total	$ 526,502	$ 184,484
Fair Value
Held to maturity, fair value, total	518,464	192,179
Amortized Cost
Available for sale, amortized cost, total	1,539,560	1,371,539
Fair Value
Available for sale, fair value, total	1,546,155	1,398,157
Other debt
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	1,418
Available for sale, amortized cost, due after one year through five years	13,892
Available for sale, amortized cost, due after five years through ten years	8,376
Available for sale, amortized cost, due after ten years	15,115
Available for sale, amortized cost, total	38,801
Fair Value
Available for sale, fair value, due in less than one year	1,442
Available for sale, fair value, due after one year through five years	14,828
Available for sale, fair value, due after five years through ten years	8,764
Available for sale, fair value, due after ten years	15,916
Available for sale, fair value, total	40,950
Mortgage-backed securities and collateralized mortgage obligations of U.S. government-sponsored entities
Amortized Cost
Held to maturity, amortized cost, total	526,502
Fair Value
Held to maturity, fair value, total	518,464	192,179
Amortized Cost
Available for sale, amortized cost, total	1,147,743	1,038,437
Fair Value
Available for sale, fair value, total	1,150,671	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	75,754	89,284
Fair Value
Available for sale, fair value, total	77,228	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	277,262	202,563
Fair Value
Available for sale, fair value, total	$ 277,306	$ 202,195