Investment Securities Held to Maturity Securities by Type (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	$ 410,430	$ 422,096
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	38	345
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(10,940)	(4,192)
Securities held to maturity, fair value	399,528	418,249
US Government Agencies Residential Mortgage-backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	3,895	3,925
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(109)	(14)
Securities held to maturity, fair value	3,786	3,911
US Government Agency Debt Securities Commercial [Domain]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	57,762	58,249
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(2,224)	(1,394)
Securities held to maturity, fair value	55,538	56,855
Residential Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	294,205	305,126
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	10
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(7,645)	(2,552)
Securities held to maturity, fair value	286,560	302,584
Obligations of U.S. Government-Sponsored Enterprises - Mortgage-Backed Securities - Commercial [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	13,859	14,056
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(299)	(71)
Securities held to maturity, fair value	13,560	13,985
Obligations of States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	40,509	40,540
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	38	335
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(660)	(161)
Securities held to maturity, fair value	39,887	40,714
Foreign Government Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	200	200
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(3)	0
Securities held to maturity, fair value	$ 197	$ 200