Investment Securities - (Summary of Held-to-maturity Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	$ 313,446	$ 332,505
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	1,374	1,701
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(1,550)	(1,633)
Fair value	313,270	332,573
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]
Held-to-maturity Securities	247,775	263,411
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	1,367	1,685
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(202)	(234)
Fair value	248,940	264,862
Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	65,671	69,094
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	7	16
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(1,348)	(1,399)
Fair value	$ 64,330	$ 67,711