Note Fair value measurement (Changes in level 3 assets and liabilities measured at fair value on a recurring basis) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	$ 195,766	$ 212,378	$ 204,959	$ 221,811
Gains (Losses) included in earnings	(10,342)	(6,101)	(24,439)	(18,863)
Gains (losses) included in OCI	(1)	(1)	9	15
Additions	1,722	2,987	7,901	9,133
Sales	0	(110)	(521)	(2,134)
Settlements	(372)	(158)	(1,048)	(967)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(4,164)	0	(4,252)	0
Ending Balance	182,609	208,995	182,609	208,995
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	(6,239)	(1,093)	(9,869)	(4,208)
Liabilities, Fair Value Disclosure [Abstract]
Beginning Balance	(163,668)	(128,511)	(153,158)	(120,380)
Gains (Losses) included in earnings	(3,208)	(6,611)	(13,718)	(14,742)
Gains (losses) included in OCI	0	0	0	0
Additions	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Transfer into Level 3	0	0	0	0
Transfer out of Level 3	0	0	0	0
Ending Balance	(166,876)	(135,122)	(166,876)	(135,122)
Fair Value Liabilities Measured On Recurring Basis Change In Unrealized Gain Loss	(3,208)	(6,611)	(13,718)	(14,742)
Other liabilities | Contingent consideration
Liabilities, Fair Value Disclosure [Abstract]
Beginning Balance	(163,668)	(128,511)	(153,158)	(120,380)
Gains (Losses) included in earnings	(3,208)	(6,611)	(13,718)	(14,742)
Gains (losses) included in OCI	0	0	0	0
Additions	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Transfer out of Level 3	0		0
Ending Balance	(166,876)	(135,122)	(166,876)	(135,122)
Fair Value Liabilities Measured On Recurring Basis Change In Unrealized Gain Loss	(3,208)	(6,611)	(13,718)	(14,742)
Available For Sale Securities | Mortgage Backed Securities
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	1,289	1,398	1,392	1,434
Gains (Losses) included in earnings	0	0	0	(2)
Gains (losses) included in OCI	(1)	(1)	9	15
Additions	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	(25)	(50)
Transfers out of Level 3	0		(88)
Ending Balance	1,288	1,397	1,288	1,397
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	0	0	0	0
Trading account securities | Mortgage Backed Securities
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	4,334	5,364	4,755	6,454
Gains (Losses) included in earnings	(77)	(32)	(124)	85
Gains (losses) included in OCI	0	0	0	0
Additions	0	128	332	1,076
Sales	0	(110)	(156)	(1,826)
Settlements	(326)	(100)	(876)	(539)
Transfers out of Level 3	(3,888)		(3,888)
Ending Balance	43	5,250	43	5,250
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	0	(29)	(23)	74
Trading account securities | Collateralized Mortgage Obligations
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	858	1,399	1,321	1,831
Gains (Losses) included in earnings	5	10	0	(3)
Gains (losses) included in OCI	0	0	0	0
Additions	31	5	39	214
Sales	0	0	(365)	(308)
Settlements	(46)	(43)	(147)	(363)
Transfers out of Level 3	(276)		(276)
Ending Balance	572	1,371	572	1,371
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	1	10	(5)	4
Trading account securities | Other
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	557	640	602	687
Gains (Losses) included in earnings	(8)	(17)	(53)	(64)
Gains (losses) included in OCI	0	0	0	0
Additions	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Transfers out of Level 3	0		0
Ending Balance	549	623	549	623
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	1	8	22	29
Mortgage Servicing Rights
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	188,728	203,577	196,889	211,405
Gains (Losses) included in earnings	(10,262)	(6,062)	(24,262)	(18,879)
Gains (losses) included in OCI	0	0	0	0
Additions	1,691	2,854	7,530	7,843
Sales	0	0	0	0
Settlements	0	(15)	0	(15)
Transfers out of Level 3	0		0
Ending Balance	180,157	200,354	180,157	200,354
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	$ (6,241)	$ (1,082)	$ (9,863)	$ (4,315)