Past Due Loans, Allowance For Credit Losses, Impaired Loans and TDRS (Details) - Credit Quality Indicators by Class, Excluding Covered Loans - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Commercial And Industrial
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		$ 2,392,860	$ 2,253,556
Commercial And Industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		2,247,010	2,115,170
Commercial And Industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	90,414	84,615
Commercial And Industrial | Substandard Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	48,998	31,078
Commercial And Industrial | Substandard Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		6,438	22,693	[4]
Agricultural
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		393,732	358,249
Agricultural | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		388,034	357,595
Agricultural | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	0	294
Agricultural | Substandard Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	5,586	0
Agricultural | Substandard Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		112	360	[4]
Office Retail and Industrial
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		1,414,077	1,478,379
Office Retail and Industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		1,335,648	1,393,885
Office Retail and Industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	37,420	38,891
Office Retail and Industrial | Substandard Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	34,048	32,664
Office Retail and Industrial | Substandard Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		6,961	12,939	[4]
Multi-Family
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		539,308	564,421
Multi-Family | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		527,520	553,255
Multi-Family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	6,147	6,363
Multi-Family | Substandard Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	4,595	4,049
Multi-Family | Substandard Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		1,046	754	[4]
Construction
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		192,086	204,236
Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		173,821	178,992
Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	5,181	5,776
Construction | Substandard Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	9,752	12,487
Construction | Substandard Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		3,332	6,981	[4]
Other Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		869,748	887,897
Other Commercial Real Estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		829,347	829,003
Other Commercial Real Estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	24,140	32,517
Other Commercial Real Estate | Substandard Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	10,363	19,407
Other Commercial Real Estate | Substandard Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		5,898	6,970	[4]
Total Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		3,015,219	3,134,933
Total Commercial Real Estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		2,866,336	2,955,135
Total Commercial Real Estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	72,888	83,547
Total Commercial Real Estate | Substandard Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	58,758	68,607
Total Commercial Real Estate | Substandard Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[4]	17,237	27,644
Total Corporate Loans
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		5,801,811	5,746,738
Total Corporate Loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		5,501,380	5,427,900
Total Corporate Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	163,302	168,456
Total Corporate Loans | Substandard Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	113,342	99,685
Total Corporate Loans | Substandard Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[4]	$ 23,787	$ 50,697

[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.

[2] Total special mention and substandard loans includes accruing TDRs of $870,000 as of September 30, 2015 and $1.8 million as of December 31, 2014.

[3] 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] 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.