Securities - Components of Available for Sale Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 572,764	$ 566,509
Available-for-sale securities, Gross unrealized gains	947	8,763
Available-for-sale securities, Gross unrealized losses	(30,900)	(710)
Total fair value	542,811	574,562
U.S. Treasury and Government Sponsored Entities' Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	250,268	161,845
Available-for-sale securities, Gross unrealized gains	1	2,409
Available-for-sale securities, Gross unrealized losses	(20,506)	(562)
Total fair value	229,763	163,692
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	101	101
Available-for-sale securities, Gross unrealized gains	295	212
Available-for-sale securities, Gross unrealized losses
Total fair value	396	313
Mortgage-backed GSE Securities: Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	322,395	404,563
Available-for-sale securities, Gross unrealized gains	651	6,142
Available-for-sale securities, Gross unrealized losses	(10,394)	(148)
Total fair value	$ 312,652	$ 410,557