Investment Securities Held to Maturity Securities by Type (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	$ 436,081	$ 372,513
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	770	60
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(1,969)	(3,955)
Securities held to maturity, fair value	434,882	368,618
US Government Agencies Residential Mortgage-backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	4,113	4,297
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	5	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	(4)
Securities held to maturity, fair value	4,118	4,293
US Government Agency Debt Securities Commercial [Domain]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	58,528	34,444
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(861)	(561)
Securities held to maturity, fair value	57,667	33,883
Residential Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	318,442	280,430
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	367	5
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(975)	(2,527)
Securities held to maturity, fair value	317,834	277,908
Obligations of U.S. Government-Sponsored Enterprises - Mortgage-Backed Securities - Commercial [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	14,226	14,675
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(4)	(142)
Securities held to maturity, fair value	14,222	14,533
Obligations of States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	40,572	38,667
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	398	55
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(129)	(721)
Securities held to maturity, fair value	40,841	38,001
Foreign Government Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	200	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Securities held to maturity, fair value	$ 200	$ 0