Note Fair value measurement (Quantitative inputs level 3) (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Assets, Fair Value Disclosure [Abstract]
Trading Securities Debt		$ 42,386		$ 33,926
Servicing Asset At Fair Value Amount		$ 166,281	$ 193,698	168,031	$ 196,889
Fair Value Inputs Quantitative Information [Abstract]
Discount Rate		4.57%	5.47%
Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Trading Securities Debt		$ 42,308		33,746
Servicing Asset At Fair Value Amount		166,281		168,031
Liabilities, Fair Value Disclosure [Abstract]
Contingent consideration		(170,970)		(164,858)
Fair Value, Measurements, Nonrecurring
Assets, Fair Value Disclosure [Abstract]
Loans Receivable, Fair Value Disclosure	[1]	29,826	$ 45,133
Real Estate Acquired Through Foreclosure	[2]	14,397	$ 17,155
Contingent consideration | Fair Value, Measurements, Recurring | Fair Value Inputs Level 3 Internal Valuation Technique
Liabilities, Fair Value Disclosure [Abstract]
Contingent consideration		$ (170,970)
Fair Value Inputs [Abstract]
Fair Value Measurements, Valuation Techniques		Discounted cash flow model
Unobservable Inputs		Credit loss rate on covered loans / Risk premium component of discount rate
Contingent consideration | Fair Value, Measurements, Recurring | Maximum | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Credit Loss Rate		100.00%
Contingent consideration | Fair Value, Measurements, Recurring | Minimum | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Credit Loss Rate		0.00%
Contingent consideration | Fair Value, Measurements, Recurring | Weighted Average | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Credit Loss Rate		3.40%
Contingent consideration | Fair Value, Measurements, Recurring | Risk Premium | Weighted Average | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Discount Rate		2.30%
Mortgage Servicing Rights | Fair Value, Measurements, Recurring | Fair Value Inputs Level 3 Internal Valuation Technique
Assets, Fair Value Disclosure [Abstract]
Servicing Asset At Fair Value Amount		$ 166,281
Fair Value Inputs [Abstract]
Fair Value Measurements, Valuation Techniques		Discounted cash flow model
Unobservable Inputs		Prepayment speed / Weighted average life / Discount rate
Mortgage Servicing Rights | Fair Value, Measurements, Recurring | Maximum | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Prepayment speed		15.90%
Weighted average life (in years)		16 years 5 months
Discount Rate		15.00%
Mortgage Servicing Rights | Fair Value, Measurements, Recurring | Minimum | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Prepayment speed		0.20%
Weighted average life (in years)		1 month
Discount Rate		9.50%
Mortgage Servicing Rights | Fair Value, Measurements, Recurring | Weighted Average | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Prepayment speed		4.80%
Weighted average life (in years)		7 years 1 month
Discount Rate		11.20%
Loan | Fair Value, Measurements, Nonrecurring | Fair Value Inputs Level 3 Internal Valuation Technique
Assets, Fair Value Disclosure [Abstract]
Loans Receivable, Fair Value Disclosure		$ 26,937
Fair Value Inputs [Abstract]
Fair Value Measurements, Valuation Techniques		External appraisal
Unobservable Inputs		Haircut applied on external appraisals
Loan | Fair Value, Measurements, Nonrecurring | Weighted Average | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Haircut Applied On External Appraisal		25.00%
Other real estate owned | Fair Value, Measurements, Nonrecurring | Fair Value Inputs Level 3 Internal Valuation Technique
Assets, Fair Value Disclosure [Abstract]
Real Estate Acquired Through Foreclosure		$ 12,525
Fair Value Inputs [Abstract]
Fair Value Measurements, Valuation Techniques		External appraisal
Unobservable Inputs		Haircut applied on external appraisals
Other real estate owned | Fair Value, Measurements, Nonrecurring | Maximum | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Haircut Applied On External Appraisal		30.00%
Other real estate owned | Fair Value, Measurements, Nonrecurring | Minimum | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Haircut Applied On External Appraisal		15.00%
Other real estate owned | Fair Value, Measurements, Nonrecurring | Weighted Average | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Haircut Applied On External Appraisal		23.80%
Collateralized Mortgage Obligations | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Trading Securities Debt		$ 488		529
Collateralized Mortgage Obligations | Trading account securities | Fair Value, Measurements, Recurring | Fair Value Inputs Level 3 Internal Valuation Technique
Assets, Fair Value Disclosure [Abstract]
Trading Securities Debt		$ 488
Fair Value Inputs [Abstract]
Fair Value Measurements, Valuation Techniques		Discounted cash flow model
Unobservable Inputs		Weighted average life / Yield / Constant prepayment rate
Collateralized Mortgage Obligations | Trading account securities | Fair Value, Measurements, Recurring | Maximum | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Weighted Average Life		2 years 4 months
Yield		4.20%
Constant Prepayment Rate		21.40%
Collateralized Mortgage Obligations | Trading account securities | Fair Value, Measurements, Recurring | Minimum | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Weighted Average Life		1 year 6 months
Yield		3.70%
Constant Prepayment Rate		16.70%
Collateralized Mortgage Obligations | Trading account securities | Fair Value, Measurements, Recurring | Weighted Average | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Weighted Average Life		2 years 1 month
Yield		3.90%
Constant Prepayment Rate		18.60%
Other | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Trading Securities Debt		$ 3,489		$ 3,517
Other | Trading account securities | Fair Value, Measurements, Recurring | Fair Value Inputs Level 3 Internal Valuation Technique
Assets, Fair Value Disclosure [Abstract]
Trading Securities Debt		$ 519
Fair Value Inputs [Abstract]
Fair Value Measurements, Valuation Techniques		Discounted cash flow model
Unobservable Inputs		Weighted average life / Yield / Constant prepayment rate
Other | Trading account securities | Fair Value, Measurements, Recurring | Weighted Average | Fair Value Inputs Level 3 Internal Valuation Technique
Fair Value Inputs Quantitative Information [Abstract]
Weighted Average Life		5 years 4 months
Yield		12.30%
Constant Prepayment Rate		10.80%

[1] Relates mostly to certain impaired collateral dependent loans. The impairment was measured based on the fair value of the collateral, which is derived from appraisals that take into consideration prices in observed transactions involving similar assets in similar locations, in accordance with the provisions of ASC Section 310-10-35 . Costs to sell are excluded from the reported fair value amount .

[2] Represents the fair value of foreclosed real estate and other collateral owned that were written d own to their fair value. Costs to sell are excluded from the reported fair value amount.