Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held to maturity, amortized cost, total	$ 295,485	$ 357,949
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held to maturity, fair value, total	291,340	349,895
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available for sale, amortized cost, total	882,557	882,872
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available for sale, fair value, total	877,549	865,831
Mortgage-backed securities and collateralized mortgage obligations of U.S. Government Sponsored Entities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held to maturity, amortized cost, total	295,485
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held to maturity, fair value, total	291,340	297,099
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available for sale, amortized cost, total	528,404	567,753
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available for sale, fair value, total	523,953	554,006
Private mortgage-backed securities and collateralized mortgage obligations
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held to maturity, amortized cost, total	0
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held to maturity, fair value, total	0	21,673
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available for sale, amortized cost, total	67,206	55,569
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available for sale, fair value, total	67,935	$ 55,728
Collateralized loan obligations
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
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
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
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
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available for sale, amortized cost, due in less than one year	11,288
Available for sale, amortized cost, due after one year through five years	102,835
Available for sale, amortized cost, due after five years through ten years	169,369
Available for sale, amortized cost, due after ten years	3,455
Available for sale, amortized cost, total	286,947
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available for sale, fair value, due in less than one year	11,268
Available for sale, fair value, due after one year through five years	102,588
Available for sale, fair value, due after five years through ten years	168,212
Available for sale, fair value, due after ten years	3,593
Available for sale, fair value, total	$ 285,661