Fair Value Measurements (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Fair value assets and liabilities measured on recurring and nonrecurring basis
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
Assets
Securities available-for-sale	5,309,187		5,309,187		$ 5,882,983
Trading securities	154,706		154,706		173,188
Liabilities
FDIC clawback liability	16,608		16,608
Redeemable noncontrolling interest	32,847		32,847		39,978
U.S. Treasury
Assets
Securities available-for-sale	390,329		390,329		116,926
Federal agency - Debt
Assets
Securities available-for-sale	286,360		286,360		1,398,581
Federal agency - MBS
Assets
Securities available-for-sale	92,881		92,881		104,526
CMOs - Federal agency
Assets
Securities available-for-sale	3,536,128		3,536,128		3,580,590
CMOs - Non-agency
Assets
Securities available-for-sale	20,431		20,431		24,014
State and municipal
Assets
Securities available-for-sale	360,744		360,744		479,031
Other debt securities
Assets
Securities available-for-sale	622,314		622,314		176,169
Equity securities and mutual funds
Assets
Securities available-for-sale					3,146
Measured on a Recurring Basis | Quoted Prices in Active Markets Level 1
Assets
Trading securities	146,710		146,710		171,778
Derivatives assets	8,454		8,454		6,106
Total assets at fair value	545,493		545,493		297,956
Liabilities
Derivative liabilities	8,800		8,800		6,623
Total liabilities at fair value	8,800		8,800		6,623
Measured on a Recurring Basis | Quoted Prices in Active Markets Level 1 | U.S. Treasury
Assets
Securities available-for-sale	390,329		390,329		116,926
Measured on a Recurring Basis | Quoted Prices in Active Markets Level 1 | Equity securities and mutual funds
Assets
Securities available-for-sale					3,146
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2
Assets
Trading securities	7,996		7,996		1,410
Derivatives assets	71,487		71,487		44,598
Total assets at fair value	4,994,871		4,994,871		5,805,372
Liabilities
Derivative liabilities	72,976		72,976		44,686
Other liabilities	797		797		946
Total liabilities at fair value	73,773		73,773		45,632
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | Federal agency - Debt
Assets
Securities available-for-sale	286,360		286,360		1,398,581
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | Federal agency - MBS
Assets
Securities available-for-sale	92,881		92,881		104,526
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | CMOs - Federal agency
Assets
Securities available-for-sale	3,536,128		3,536,128		3,580,590
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | CMOs - Non-agency
Assets
Securities available-for-sale	20,431		20,431		24,014
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | State and municipal
Assets
Securities available-for-sale	357,274		357,274		475,484
Measured on a Recurring Basis | Significant Other Observable Inputs Level 2 | Other debt securities
Assets
Securities available-for-sale	622,314		622,314		176,169
Measured on a Recurring Basis | Significant Unobservable Inputs Level 3
Assets
Derivatives assets	2,235		2,235		882
Contingent consideration asset	2,605		2,605		2,930
Total assets at fair value	8,310		8,310		7,359
Liabilities
Contingent consideration liability	36,985		36,985		34,983
FDIC clawback liability	16,608		16,608		15,106
Total liabilities at fair value	53,593		53,593		50,089
Redeemable noncontrolling interest	$ 32,847		$ 32,847		$ 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	$ 3,470		$ 3,470		$ 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	(1,203)	$ (276)	(4,153)	$ 860
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:		7		81
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	(653)	$ (283)	(1,973)	$ 784
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	(550)		(2,180)
Measured on a Nonrecurring Basis | Significant Unobservable Inputs Level 3
Assets
Total assets at fair value	$ 11,131		$ 11,131		$ 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	$ 9,544		$ 9,544		$ 5,644
Measured on a Nonrecurring Basis | Significant Unobservable Inputs Level 3 | Private equity and alternative investments
Assets
Total assets at fair value	1,587		1,587
Fair Value
Liabilities
Total liabilities at fair value	136,200		136,200		102,300
Fair Value | Measured on a Recurring Basis
Assets
Trading securities	154,706		154,706		173,188
Derivatives assets	82,176		82,176		51,586
Contingent consideration asset	2,605		2,605		2,930
Total assets at fair value	$ 5,548,674		$ 5,548,674		$ 6,110,687
Percent of total assets	16.00%		16.00%		19.00%
Liabilities
Derivative liabilities	$ 81,776		$ 81,776		$ 51,309
Contingent consideration liability	36,985		36,985		34,983
FDIC clawback liability	16,608		16,608		15,106
Other liabilities	797		797		946
Total liabilities at fair value	136,166		136,166		102,344
Redeemable noncontrolling interest	32,847		32,847		39,978
Fair Value | Measured on a Recurring Basis | U.S. Treasury
Assets
Securities available-for-sale	390,329		390,329		116,926
Fair Value | Measured on a Recurring Basis | Federal agency - Debt
Assets
Securities available-for-sale	286,360		286,360		1,398,581
Fair Value | Measured on a Recurring Basis | Federal agency - MBS
Assets
Securities available-for-sale	92,881		92,881		104,526
Fair Value | Measured on a Recurring Basis | CMOs - Federal agency
Assets
Securities available-for-sale	3,536,128		3,536,128		3,580,590
Fair Value | Measured on a Recurring Basis | CMOs - Non-agency
Assets
Securities available-for-sale	20,431		20,431		24,014
Fair Value | Measured on a Recurring Basis | State and municipal
Assets
Securities available-for-sale	360,744		360,744		479,031
Fair Value | Measured on a Recurring Basis | Other debt securities
Assets
Securities available-for-sale	622,314		622,314		176,169
Fair Value | Measured on a Recurring Basis | Equity securities and mutual funds
Assets
Securities available-for-sale					3,146
Fair Value | Measured on a Nonrecurring Basis
Assets
Total assets at fair value	11,131		11,131		5,644
Fair Value | Measured on a Nonrecurring Basis | Other real estate owned
Assets
Total assets at fair value	9,544		9,544		$ 5,644
Fair Value | Measured on a Nonrecurring Basis | Private equity and alternative investments
Assets
Total assets at fair value	$ 1,587		$ 1,587