Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 2,436,131,000	$ 2,436,131,000
Amortization of core deposit intangibles	5,344,000	8,297,000	$ 15,784,000
Impairment losses of intangible assets	0	0	$ 0
Mortgage servicing rights	$ 247,734,000	227,297,000
Increase in primary mortgage rate to refinance	0.06%
Mortgage Receivable
Finite-Lived Intangible Assets [Line Items]
Unpaid principal balance of loans serviced for others	$ 24,200,000,000	$ 22,400,000,000
Core deposit intangibles | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization period for core deposit intangibles (in years)	10 years