Fair Value Measurements (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Fair Value Measurements
Fair value of assets transfers from Level 1 to Level 2	$ 0		$ 0
Fair value of assets transfers from Level 2 to Level 1	0		0
Fair value of liabilities transfers from Level 1 to Level 2	0		0
Fair value of liabilities transfers from Level 2 to Level 1	0		0
Assets
Securities available-for-sale	4,940,843		4,940,843		$ 5,882,983
Trading securities	110,136		110,136		173,188
Liabilities
FDIC clawback liability	16,289		16,289
Redeemable noncontrolling interest	37,755		37,755		39,978
U.S. Treasury
Assets
Securities available-for-sale	148,308		148,308		116,926
Federal agency - Debt
Assets
Securities available-for-sale	899,934		899,934		1,398,581
Federal agency - MBS
Assets
Securities available-for-sale	96,878		96,878		104,526
CMOs - Federal agency
Assets
Securities available-for-sale	3,286,076		3,286,076		3,580,590
CMOs - Non-agency
Assets
Securities available-for-sale	21,731		21,731		24,014
State and municipal
Assets
Securities available-for-sale	400,055		400,055		479,031
Other debt securities
Assets
Securities available-for-sale	87,395		87,395		176,169
Equity securities and mutual funds
Assets
Securities available-for-sale	466		466		3,146
Fair Value
Liabilities
Total liabilities at fair value	103,300		103,300		102,300
Measured on a Recurring Basis | Fair Value
Assets
Trading securities	110,136		110,136		173,188
Derivatives assets	51,671		51,671		51,586
Contingent consideration asset	2,605		2,605		2,930
Total assets at fair value	$ 5,105,255		$ 5,105,255		$ 6,110,687
Percent of total assets	15.00%		15.00%		19.00%
Liabilities
Derivative liabilities	$ 49,587		$ 49,587		$ 51,309
Contingent consideration liability	36,573		36,573		34,983
FDIC clawback liability	16,289		16,289		15,106
Other liabilities	850		850		946
Total liabilities at fair value	103,299		103,299		102,344
Redeemable noncontrolling interest	37,755		37,755		39,978
Measured on a Recurring Basis | Fair Value | U.S. Treasury
Assets
Securities available-for-sale	148,308		148,308		116,926
Measured on a Recurring Basis | Fair Value | Federal agency - Debt
Assets
Securities available-for-sale	899,934		899,934		1,398,581
Measured on a Recurring Basis | Fair Value | Federal agency - MBS
Assets
Securities available-for-sale	96,878		96,878		104,526
Measured on a Recurring Basis | Fair Value | CMOs - Federal agency
Assets
Securities available-for-sale	3,286,076		3,286,076		3,580,590
Measured on a Recurring Basis | Fair Value | CMOs - Non-agency
Assets
Securities available-for-sale	21,731		21,731		24,014
Measured on a Recurring Basis | Fair Value | State and municipal
Assets
Securities available-for-sale	400,055		400,055		479,031
Measured on a Recurring Basis | Fair Value | Other debt securities
Assets
Securities available-for-sale	87,395		87,395		176,169
Measured on a Recurring Basis | Fair Value | Equity securities and mutual funds
Assets
Securities available-for-sale	466		466		3,146
Measured on a Recurring Basis | Quoted Prices in Active Markets Level 1
Assets
Trading securities	103,999		103,999		171,778
Derivatives assets	6,597		6,597		6,106
Total assets at fair value	259,370		259,370		297,956
Liabilities
Derivative liabilities	6,235		6,235		6,623
Total liabilities at fair value	6,235		6,235		6,623
Measured on a Recurring Basis | Quoted Prices in Active Markets Level 1 | U.S. Treasury
Assets
Securities available-for-sale	148,308		148,308		116,926
Measured on a Recurring Basis | Quoted Prices in Active Markets Level 1 | Equity securities and mutual funds
Assets
Securities available-for-sale	466		466		3,146
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2
Assets
Trading securities	6,137		6,137		1,410
Derivatives assets	43,201		43,201		44,598
Total assets at fair value	4,837,861		4,837,861		5,805,372
Liabilities
Derivative liabilities	43,352		43,352		44,686
Other liabilities	850		850		946
Total liabilities at fair value	44,202		44,202		45,632
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | Federal agency - Debt
Assets
Securities available-for-sale	899,934		899,934		1,398,581
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | Federal agency - MBS
Assets
Securities available-for-sale	96,878		96,878		104,526
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | CMOs - Federal agency
Assets
Securities available-for-sale	3,286,076		3,286,076		3,580,590
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | CMOs - Non-agency
Assets
Securities available-for-sale	21,731		21,731		24,014
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | State and municipal
Assets
Securities available-for-sale	396,509		396,509		475,484
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | Other debt securities
Assets
Securities available-for-sale	87,395		87,395		176,169
Measured on a Recurring Basis | Significant Unobservable Inputs Level 3
Assets
Derivatives assets	1,873		1,873		882
Contingent consideration asset	2,605		2,605		2,930
Total assets at fair value	8,024		8,024		7,359
Liabilities
Contingent consideration liability	36,573		36,573		34,983
FDIC clawback liability	16,289		16,289		15,106
Total liabilities at fair value	52,862		52,862		50,089
Redeemable noncontrolling interest	$ 37,755		$ 37,755		$ 39,978
Measured on a Recurring Basis | Significant Unobservable Inputs Level 3 | Maximum
Assets
Percent of total assets	1.00%		1.00%		1.00%
Measured on a Recurring Basis | Significant Unobservable Inputs Level 3 | State and municipal
Assets
Securities available-for-sale	$ 3,546		$ 3,546		$ 3,547
Measured on a Nonrecurring Basis
Net (losses) gains recognized for assets measured at fair value on nonrecurring basis
Total net (losses) gains recognized	(912)	$ 1,080	(2,949)	$ 1,136
Measured on a Nonrecurring Basis | Commercial real estate mortgages
Net (losses) gains recognized for assets measured at fair value on nonrecurring basis
Collateral dependent impaired loans:				(5)
Measured on a Nonrecurring Basis | Residential mortgages
Net (losses) gains recognized for assets measured at fair value on nonrecurring basis
Collateral dependent impaired loans:		74		74
Measured on a Nonrecurring Basis | Other real estate owned
Net (losses) gains recognized for assets measured at fair value on nonrecurring basis
Total net (losses) gains recognized	318	$ 1,006	(1,319)	$ 1,067
Measured on a Nonrecurring Basis | Private equity and alternative investments
Net (losses) gains recognized for assets measured at fair value on nonrecurring basis
Total net (losses) gains recognized	(1,230)		(1,630)
Measured on a Nonrecurring Basis | Fair Value
Assets
Total assets at fair value	10,011		10,011		5,644
Measured on a Nonrecurring Basis | Fair Value | Other real estate owned
Assets
Total assets at fair value	5,577		5,577		$ 5,644
Measured on a Nonrecurring Basis | Fair Value | Private equity and alternative investments
Assets
Total assets at fair value	4,434		4,434
Measured on a Nonrecurring Basis | Significant Other Observable Inputs Level 2
Assets
Total assets at fair value	$ 635		$ 635
Measured on a Nonrecurring Basis | Significant Other Observable Inputs Level 2 | Maximum
Assets
Percent of total assets	1.00%		1.00%		1.00%
Measured on a Nonrecurring Basis | Significant Other Observable Inputs Level 2 | Other real estate owned
Assets
Total assets at fair value	$ 635		$ 635
Measured on a Nonrecurring Basis | Significant Unobservable Inputs Level 3
Assets
Total assets at fair value	$ 9,376		$ 9,376		$ 5,644
Measured on a Nonrecurring Basis | Significant Unobservable Inputs Level 3 | Maximum
Assets
Percent of total assets	1.00%		1.00%		1.00%
Measured on a Nonrecurring Basis | Significant Unobservable Inputs Level 3 | Other real estate owned
Assets
Total assets at fair value	$ 4,942		$ 4,942		$ 5,644
Measured on a Nonrecurring Basis | Significant Unobservable Inputs Level 3 | Private equity and alternative investments
Assets
Total assets at fair value	$ 4,434		$ 4,434