Investment Securities (Securities Held to Maturity by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 478,846	$ 473,684
Fair value	501,435	$ 488,331
Held-to-maturity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, amortized cost	11,723
Due after one year through five years, amortized cost	52,755
Due after five years through ten years, amortized cost	229,855
Due after ten years, amortized cost	183,321
Amortized cost	477,654
Due in one year or less, fair value	11,761
Due after one year through five years, fair value	53,903
Due after five years through ten years, fair value	242,268
Due after ten years, fair value	192,262
Fair value	$ 500,194