Investment Securities - (Summary of Held-to-Maturity Securities, Unrealized Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Fair Value, Less than 12 months	$ 37,267	$ 54,791
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(306)	(591)
Fair Value, 12 months or more	31,762	32,146
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(915)	(1,042)
Total Fair Value	69,029	86,937
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,221)	(1,633)
Residential Mortgage Pass-Through Securities Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Fair Value, Less than 12 months	19,284	27,799
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(104)	(234)
Total Fair Value	19,284	27,799
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(104)	(234)
Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Fair Value, Less than 12 months	17,983	26,992
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(202)	(357)
Fair Value, 12 months or more	31,762	32,146
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(915)	(1,042)
Total Fair Value	49,745	59,138
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (1,117)	$ (1,399)