Investment Securities - (Summary of Held-to-maturity Investment Securities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities	$ 427,503	$ 530,590
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	2,946	5,990
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(1,864)	(1,943)
Fair value	428,585	534,637
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	340,131	422,622
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	2,911	5,773
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(230)	(72)
Fair value	342,812	428,323
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	87,372	107,968
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	35	217
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(1,634)	(1,871)
Fair value	$ 85,773	$ 106,314