Changes in level 3 assets and liabilities measured at fair value on a recurring basis (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	$ 168,699	$ 174,230	$ 180,773	$ 178,057
Gains (Losses) included in earnings	(2,537)	3,887	(19,147)	(7,228)
Gains (losses) included in OCI	(20)	44	(100)	(42)
Additions	3,053	5,253	10,659	15,733
Sales	0	(203)	(1,109)	(902)
Settlements	(653)	(1,580)	(2,534)	(3,987)
Ending Balance	168,542	181,631	168,542	181,631
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	2,633	9,478	(3,813)	13,442
Liabilities, Fair Value Disclosure [Abstract]
Beginning Balance	(127,551)	(119,253)	(128,299)	(112,002)
Gains (Losses) included in earnings	1,078	(5,322)	1,040	(12,573)
Gains (losses) included in OCI	0	0	0	0
Additions	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	786	0
Ending Balance	(126,473)	(124,575)	(126,473)	(124,575)
Fair Value Liabilities Measured On Recurring Basis Change In Unrealized Gain Loss	1,078	(5,322)	1,040	(12,573)
Other Liabilities Member | Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Contingent Liability [Member]
Liabilities, Fair Value Disclosure [Abstract]
Beginning Balance	(127,551)	(119,253)	(128,299)	(112,002)
Gains (Losses) included in earnings	1,078	(5,322)	1,040	(12,573)
Gains (losses) included in OCI	0	0	0	0
Additions	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	786	0
Ending Balance	(126,473)	(124,575)	(126,473)	(124,575)
Fair Value Liabilities Measured On Recurring Basis Change In Unrealized Gain Loss	1,078	(5,322)	1,040	(12,573)
Available For Sale Securities Member | Collateralized Mortgage Backed Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	6,169	6,756	6,523	7,070
Gains (Losses) included in earnings	(1)	(2)	(4)	(5)
Gains (losses) included in OCI	(20)	44	(100)	(42)
Additions	0	0	0	0
Sales	0	0	0	0
Settlements	(222)	(100)	(493)	(325)
Ending Balance	5,926	6,698	5,926	6,698
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	0	0	0	0
Trading Account Assets[Member] | Collateralized Mortgage Backed Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	7,802	10,335	9,799	11,818
Gains (Losses) included in earnings	(20)	83	(134)	(91)
Gains (losses) included in OCI	0	0	0	0
Additions	127	343	778	601
Sales	0	(100)	(1,109)	(100)
Settlements	(376)	(625)	(1,801)	(2,192)
Ending Balance	7,533	10,036	7,533	10,036
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	(4)	135	(70)	90
Trading Account Assets[Member] | Collateralized Mortgage Obligations Member
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	1,494	1,653	1,423	2,499
Gains (Losses) included in earnings	2	(4)	(9)	(3)
Gains (losses) included in OCI	0	0	0	0
Additions	7	0	270	25
Sales	0	(103)	0	(802)
Settlements	(55)	(67)	(236)	(240)
Ending Balance	1,448	1,479	1,448	1,479
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	2	1	(5)	4
Trading Account Assets[Member] | Other Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	1,283	2,042	1,929	2,240
Gains (Losses) included in earnings	70	(69)	(576)	(267)
Gains (losses) included in OCI	0	0	0	0
Additions	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Ending Balance	1,353	1,973	1,353	1,973
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	107	0	(424)	(7)
Mortgage Servicing Rights Member
Assets, Fair Value Disclosure [Abstract]
Beginning Balance	151,951	153,444	161,099	154,430
Gains (Losses) included in earnings	(2,588)	3,879	(18,424)	(6,862)
Gains (losses) included in OCI	0	0	0	0
Additions	2,919	4,910	9,611	15,107
Sales	0	0	0	0
Settlements	0	(788)	(4)	(1,230)
Ending Balance	152,282	161,445	152,282	161,445
Fair Value Assets Measured On Recurring Basis Change In Unrealized Gain Loss	$ 2,528	$ 9,342	$ (3,314)	$ 13,355