Investment Securities - (Summary of Unrealized Losses) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value	$ 176,709	$ 88,871
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(920)	(2,053)
12 months or more, Fair Value	575,954	757,117
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(19,012)	(19,708)
Total, Fair Value	752,663	845,988
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(19,932)	(21,761)
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	109,182	17
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(516)
12 months or more, Fair Value		89,749
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(43)
Total, Fair Value	109,182	89,766
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(516)	(43)
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	67,527	88,854
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(404)	(2,053)
12 months or more, Fair Value	575,954	667,368
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(19,012)	(19,665)
Total, Fair Value	643,481	756,222
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (19,416)	$ (21,718)