Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Allowance for loan losses	$ 47,485	$ 44,382
Depreciation	12,432	15,661
Employee benefits	16,121	16,104
Investment securities, including other-than-temporary impairment losses	17,272	18,697
Net operating loss carryforwards	46,667	57,722
Purchase accounting	33,172	40,585
Other	22,183	21,310
Total deferred tax assets	195,332	214,461
Deferred tax liabilities:
Pension plans	24,575	18,861
Other investments	20,831	15,720
Other	20,418	21,449
Total deferred tax liabilities	65,824	56,030
Net deferred tax asset (included in other assets)	$ 129,508	$ 158,431