Investment Securities (Securities Held to Maturity by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 489,114	$ 488,183
Fair value	492,863	$ 489,287
Held-to-maturity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, amortized cost	22,570
Due after one year through five years, amortized cost	56,055
Due after five years through ten years, amortized cost	250,371
Due after ten years, amortized cost	159,438
Amortized cost	488,434
Due in one year or less, fair value	22,609
Due after one year through five years, fair value	56,920
Due after five years through ten years, fair value	254,015
Due after ten years, fair value	158,614
Fair value	$ 492,158