Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Components Of Deferred Tax Assets And Liabilities [Line Items]
Allowance for loan losses	$ 53,407	$ 54,880
Depreciation	4,972	1,666
Pension plans	5,075	2,771
Employee benefits	11,775	9,102
Investment securities, including other-than-temporary impairment losses	24,196	35,569
Net operating loss carryforwards	62,053	63,806
Purchase accounting	14,251
Accrued interest	12,515	9,050
Other	23,416	20,869
Total deferred tax assets	211,660	197,713
Purchase accounting		8,727
Other investments	11,182	6,614
Deferred income	15,886
Other	13,353	10,164
Total deferred tax liabilities	40,421	25,505
Net deferred tax asset (included in other assets)	$ 171,239	$ 172,208