Goodwill and Other Intangible Assets - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0	$ 0	$ 0	$ 0
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	169,371,000		169,371,000			$ 126,621,000
Amortization of other intangible assets	4,617,000	2,562,000	$ 8,910,000	5,098,000
Core Deposits
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years			10 years
Gross intangible assets	80,470,000		$ 80,470,000		$ 44,600,000	43,396,000
Loan servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	84,956,000		$ 84,956,000		$ 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		$ 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	$ 0	$ 0