Goodwill and Other Intangible Assets - Other Intangible Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$ 167,294		$ 126,621
Accumulated Amortization	(80,563)		(83,643)
Valuation Allowance	(244)		(471)
Net Intangible Assets	86,487		42,507
Loan servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	82,879	$ 1,400	79,138
Accumulated Amortization	(58,440)		(57,054)
Valuation Allowance	(244)		(471)
Net Intangible Assets	24,195		21,613
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	80,470	$ 44,600	43,396
Accumulated Amortization	(19,911)		(24,297)
Valuation Allowance	0		0
Net Intangible Assets	60,559		19,099
Other
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	3,945		4,087
Accumulated Amortization	(2,212)		(2,292)
Valuation Allowance	0		0
Net Intangible Assets	$ 1,733		$ 1,795