Investment Securities - Amortized Cost and Fair Values of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 372,513	$ 384,324
Gross Unrealized Gains	60	331
Gross Unrealized Losses	(3,955)	(2,314)
Estimated Fair Value	368,618	382,341
Obligations of U.S. Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	38,667	31,910
Gross Unrealized Gains	55	301
Gross Unrealized Losses	(721)	(58)
Estimated Fair Value	38,001	32,153
Mortgage - Backed Securities - Residential [Member] | US Government Agencies Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	4,297	4,775
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4)	(7)
Estimated Fair Value	4,293	4,768
Mortgage - Backed Securities - Residential [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	280,430	315,609
Gross Unrealized Gains	5	30
Gross Unrealized Losses	(2,527)	(1,824)
Estimated Fair Value	277,908	313,815
Mortgage - Backed Securities - Commercial [Member] | US Government Agencies Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	34,444	16,843
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(561)	(247)
Estimated Fair Value	33,883	16,596
Mortgage - Backed Securities - Commercial [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	14,675	15,187
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(142)	(178)
Estimated Fair Value	$ 14,533	$ 15,009