Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0	$ 0
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	167,294,000			$ 126,621,000
Amortization of other intangible assets	$ 4,293,000	2,536,000
Core Deposits
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	10 years
Gross intangible assets	$ 80,470,000		$ 44,600,000	43,396,000
Loan servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	$ 82,879,000		$ 1,400,000	79,138,000
Other
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	20 years
Gross intangible assets	$ 3,945,000			$ 4,087,000
Core Deposits and Other
Finite-Lived Intangible Assets [Line Items]
Impairment of core deposits and other intangibles	$ 0	$ 0