Goodwill and Other Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill And Other Intangible Assets [Line Items]
Useful lives of core deposit and other intangible assets	8 years
Remaining weighted-average amortization period	2 years
Amortization of core deposit and other intangible assets	$ 33,824,000	$ 46,912,000	$ 60,631,000
Core Deposit and Other Intangible Assets [Member]
Goodwill And Other Intangible Assets [Line Items]
Amortization of core deposit and other intangible assets	$ 33,824,000	$ 46,912,000	$ 60,631,000
Minimum [Member]
Goodwill And Other Intangible Assets [Line Items]
Useful lives of core deposit and other intangible assets	5 years
Maximum [Member]
Goodwill And Other Intangible Assets [Line Items]
Useful lives of core deposit and other intangible assets	10 years