Investment Securities Schedule of Held-to-Maturity Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Due within 1 year	$ 87
Held-to-maturity Securities, Debt Maturities, Next Twelve Months, Fair Value	86
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	38	$ 345
Held-to-maturity Securities	410,430	422,096
Securities held to maturity, fair value	399,528	$ 418,249
Due after 1 but within 5 years	3,646
Due after 5 but within 10 years	35,350
Held-to-maturity Securities, Debt Maturities, Year Six Through Ten, Fair Value	34,764
Held-to-maturity Securities, Debt Maturities, Year Two Through Five, Fair Value	3,626
Due after 10 years	1,626
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value	1,608
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis	40,709
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value	40,084
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Net Carrying Amount	369,721
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	359,444
US Government Agencies Residential Mortgage-backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	61,700
Securities held to maturity, fair value	59,300
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	308,100
Securities held to maturity, fair value	$ 300,100