Investment Securities - (Summary of Held-to-maturity Investment Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	$ 294,891	$ 332,505
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	1,343	1,701
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(1,365)	(1,633)
Fair value	294,869	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	233,026	263,411
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	1,332	1,685
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(164)	(234)
Fair value	234,194	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	61,865	69,094
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	11	16
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(1,201)	(1,399)
Fair value	$ 60,675	$ 67,711