Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held to maturity, amortized cost, total	$ 382,137	$ 416,863
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held to maturity, fair value, total	370,787	414,470
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available for sale, amortized cost, total	976,182	953,720
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available for sale, fair value, total	954,906	949,460
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	324,410
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held to maturity, fair value, total	312,859	350,184
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available for sale, amortized cost, total	616,152	560,396
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available for sale, fair value, total	594,881	553,525
Private mortgage backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held to maturity, amortized cost, total	22,127
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held to maturity, fair value, total	22,272	23,460
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available for sale, amortized cost, total	80,618	75,152
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available for sale, fair value, total	81,132	$ 76,021
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	3,600
Held to maturity, amortized cost, due after five years through ten years	29,000
Held to maturity, amortized cost, due after ten years	3,000
Held to maturity, amortized cost, total	35,600
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	3,599
Held to maturity, fair value, due after five years through ten years	29,053
Held to maturity, fair value, due after ten years	3,004
Held to maturity, fair value, total	35,656
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available for sale, amortized cost, due in less than one year	15,119
Available for sale, amortized cost, due after one year through five years	64,674
Available for sale, amortized cost, due after five years through ten years	183,806
Available for sale, amortized cost, due after ten years	15,813
Available for sale, amortized cost, total	279,412
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available for sale, fair value, due in less than one year	15,110
Available for sale, fair value, due after one year through five years	64,761
Available for sale, fair value, due after five years through ten years	183,290
Available for sale, fair value, due after ten years	15,732
Available for sale, fair value, total	$ 278,893