Investment Securities - Securities Held to Maturity by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, Amortized cost	$ 12,442
Due after one year through five years, Amortized cost	50,288
Due after five years through ten years, Amortized cost	147,895
Due after ten years, Amortized cost	240,330
Amortized cost	454,648	357,500
Due in one year or less, Fair value	12,505
Due after one year through five years, Fair value	51,668
Due after five years through ten years, Fair value	152,984
Due after ten years, Fair value	242,254
Fair value	463,277	355,913
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	3,693	5,273
Fair value	$ 3,866	$ 5,520