Investment Securities - Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,145,778	$ 1,162,332
Gross unrealized gains	16,977	15,125
Gross unrealized losses	(5,769)	(19,863)
Fair value	1,156,986	1,157,594
Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	90,906	93,223
Gross unrealized gains	347	372
Gross unrealized losses	(45)	(179)
Fair value	91,208	93,416
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,037,367	1,060,013
Gross unrealized gains	16,353	14,493
Gross unrealized losses	(5,696)	(19,532)
Fair value	1,048,024	1,054,974
State and Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,558	8,739
Gross unrealized gains	153	171
Gross unrealized losses	(12)	(152)
Fair value	7,699	8,758
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	9,550
Gross unrealized gains	5
Gross unrealized losses	(16)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	397	357
Gross unrealized gains	119	89
Gross unrealized losses	0	0
Fair value	$ 516	$ 446