Securities - Components of Available for Sale Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 523,895	$ 551,399
Available-for-sale securities, Gross unrealized gains	45	375
Available-for-sale securities, Gross unrealized losses	(16,815)	(40,768)
Total fair value	507,125	511,006
U.S. Treasury and Government Sponsored Entities' Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	242,043	247,863
Available-for-sale securities, Gross unrealized losses	(10,404)	(25,570)
Total fair value	231,639	222,293
Mortgage-Backed GSE Securities: Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	281,852	303,435
Available-for-sale securities, Gross unrealized gains	45	31
Available-for-sale securities, Gross unrealized losses	(6,411)	(15,198)
Total fair value	275,486	288,268
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost		101
Available-for-sale securities, Gross unrealized gains		344
Total fair value		$ 445