Goodwill and Other Intangible Assets - Other Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$ 126,621	$ 138,593
Accumulated Amortization	(83,643)	(92,209)
Valuation Allowance	(471)	(900)
Net Intangible Assets	42,507	45,484
Loan servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	79,138	73,002
Accumulated Amortization	(57,054)	(52,634)
Valuation Allowance	(471)	(900)
Net Intangible Assets	21,613	19,468
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	43,396	61,504
Accumulated Amortization	(24,297)	(37,562)
Valuation Allowance	0	0
Net Intangible Assets	19,099	23,942
Other
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	4,087	4,087
Accumulated Amortization	(2,292)	(2,013)
Valuation Allowance	0	0
Net Intangible Assets	$ 1,795	$ 2,074