Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Detail) - Credit Quality Indicators by Class, Excluding Covered Loans (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Commercial Loan | Pass
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	$ 1,780,194		$ 1,558,932
Commercial Loan | Special Mention
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	23,806	[1],[2]	37,833	[1],[2]
Commercial Loan | Substandard
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	14,871	[1],[3]	8,768	[1],[3]
Commercial Loan | Non Accrual
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	11,767	[4]	25,941	[4]
Commercial Loan | Total
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	1,830,638		1,631,474
Agricultural | Pass
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	320,839		267,114
Agricultural | Special Mention
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	344	[1],[2]	331	[1],[2]
Agricultural | Substandard
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	0	[1],[3]	0	[1],[3]
Agricultural | Non Accrual
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	519	[4]	1,173	[4]
Agricultural | Total
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	321,702		268,618
Office Retail And Industrial | Pass
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	1,284,394		1,235,950
Office Retail And Industrial | Special Mention
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	28,677	[1],[2]	57,271	[1],[2]
Office Retail And Industrial | Substandard
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	23,538	[1],[3]	16,746	[1],[3]
Office Retail And Industrial | Non Accrual
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	17,076	[4]	23,224	[4]
Office Retail And Industrial | Total
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	1,353,685		1,333,191
Multi Family | Pass
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	326,901		282,126
Multi Family | Special Mention
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	3,214	[1],[2]	1,921	[1],[2]
Multi Family | Substandard
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	910	[1],[3]	0	[1],[3]
Multi Family | Non Accrual
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	1,848	[4]	1,434	[4]
Multi Family | Total
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	332,873		285,481
Construction | Pass
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	153,949		128,959
Construction | Special Mention
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	8,309	[1],[2]	26,210	[1],[2]
Construction | Substandard
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	17,642	[1],[3]	25,762	[1],[3]
Construction | Non Accrual
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	6,297	[4]	5,485	[4]
Construction | Total
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	186,197		186,416
Other Commerical Real Estate | Pass
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	761,465		712,702
Other Commerical Real Estate | Special Mention
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	14,877	[1],[2]	14,056	[1],[2]
Other Commerical Real Estate | Substandard
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	22,576	[1],[3]	30,149	[1],[3]
Other Commerical Real Estate | Non Accrual
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	8,153	[4]	16,214	[4]
Other Commerical Real Estate | Total
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	807,071		773,121
Total Commercial Real Estate | Pass
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	2,526,709		2,359,737
Total Commercial Real Estate | Special Mention
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	55,077	[1],[2]	99,458	[1],[2]
Total Commercial Real Estate | Substandard
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	64,666	[1],[3]	72,657	[1],[3]
Total Commercial Real Estate | Non Accrual
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	33,374	[4]	46,357	[4]
Total Commercial Real Estate | Total
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	2,679,826		2,578,209
Total Corporate Loans | Pass
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	4,627,742		4,185,783
Total Corporate Loans | Special Mention
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	79,227	[1],[2]	137,622	[1],[2]
Total Corporate Loans | Substandard
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	79,537	[1],[3]	81,425	[1],[3]
Total Corporate Loans | Non Accrual
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	45,660	[4]	73,471	[4]
Total Corporate Loans | Total
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	$ 4,832,166		$ 4,478,301

[1] (4) Total special mention and substandard loans includes accruing TDRs of $2.8 million as of December 31, 2013 and $448,000 as of December 31, 2012.

[2] 1) Loans categorized as special mention exhibit potential weaknesses that require the close attention of management since these potential weaknesses may result in the deterioration of repayment prospects in the future.

[3] 2) Loans categorized as substandard exhibit a well-defined weakness or weaknesses that may jeopardize the liquidation of the debt. These loans continue to accrue interest because they are well secured and collection of principal and interest is expected within a reasonable time.

[4] (3) Loans categorized as non-accrual exhibit a well-defined weakness or weaknesses that may jeopardize the liquidation of the debt or result in a loss if the deficiencies are not corrected.