Investment Securities - (Summary of Unrealized Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value	$ 110,047	$ 241,532
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,044)	(3,513)
12 months or more, Fair Value	396,893	385,707
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(11,641)	(13,025)
Total, Fair Value	506,940	627,239
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(12,685)	(16,538)
Residential Mortgage Pass-Through Securities Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value	54,344	100,898
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(387)	(530)
Total, Fair Value	54,344	100,898
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(387)	(530)
Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value	55,703	137,576
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(657)	(2,976)
12 months or more, Fair Value	396,893	385,707
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(11,641)	(13,025)
Total, Fair Value	452,596	523,283
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (12,298)	(16,001)
Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value		3,058
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(7)
Total, Fair Value		3,058
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		$ (7)