Investment Securities - (Summary of Held-to-maturity Investment Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	$ 381,172	$ 427,503
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	7,252	2,946
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(319)	(1,864)
Fair value	388,105	428,585
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	302,852	340,131
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	6,746	2,911
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		(230)
Fair value	309,598	342,812
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	78,320	87,372
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	506	35
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(319)	(1,634)
Fair value	$ 78,507	$ 85,773