Investment Securities - Investment Securities Available for Sale by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized cost	$ 23,108
Due after one year through five years, Amortized cost	78,886
Due after five years through ten years, Amortized cost	3,019
Due after ten years, Amortized cost	3,001
Amortized cost	1,145,778	1,162,332
Due in one year or less, Fair value	23,130
Due after one year through five years, Fair value	79,306
Due after five years through ten years, Fair value	3,004
Due after ten years , Fair value	3,006
Securities available for sale, at fair value	1,156,986	1,157,594
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,037,367	1,060,013
Securities available for sale, at fair value	1,048,024	1,054,974
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	397	357
Securities available for sale, at fair value	$ 516	$ 446