Past Due Loans, Allowance For Credit Losses, Impaired Loans and TDRS (Details) - Aging Analysis of Past Due Loans and Non-Performing Loans by Class - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 6,925,699	$ 6,736,853
Commercial And Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,380,931	2,230,947
30-89 Days Past Due	6,937	19,505
90 Days or More Past Due	4,992	3,104
Total Past Due	11,929	22,609
Total Loans	2,392,860	2,253,556
Non- accrual Loans	6,438	22,693
90 Days Past Due Loans, Still Accruing Interest	900	205
Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	393,574	355,982
30-89 Days Past Due	71	1,934
90 Days or More Past Due	87	333
Total Past Due	158	2,267
Total Loans	393,732	358,249
Non- accrual Loans	112	360
90 Days Past Due Loans, Still Accruing Interest	0	0
Office Retail and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,398,173	1,463,724
30-89 Days Past Due	9,642	2,340
90 Days or More Past Due	6,262	12,315
Total Past Due	15,904	14,655
Total Loans	1,414,077	1,478,379
Non- accrual Loans	6,961	12,939
90 Days Past Due Loans, Still Accruing Interest	0	76
Multi-Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	535,085	562,625
30-89 Days Past Due	1,100	1,261
90 Days or More Past Due	3,123	535
Total Past Due	4,223	1,796
Total Loans	539,308	564,421
Non- accrual Loans	1,046	754
90 Days Past Due Loans, Still Accruing Interest	2,269	83
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	188,561	197,255
30-89 Days Past Due	467	0
90 Days or More Past Due	3,058	6,981
Total Past Due	3,525	6,981
Total Loans	192,086	204,236
Non- accrual Loans	3,332	6,981
90 Days Past Due Loans, Still Accruing Interest	0	0
Other Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	858,597	876,609
30-89 Days Past Due	5,867	5,412
90 Days or More Past Due	5,284	5,876
Total Past Due	11,151	11,288
Total Loans	869,748	887,897
Non- accrual Loans	5,898	6,970
90 Days Past Due Loans, Still Accruing Interest	897	438
Total Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,980,416	3,100,213
30-89 Days Past Due	17,076	9,013
90 Days or More Past Due	17,727	25,707
Total Past Due	34,803	34,720
Total Loans	3,015,219	3,134,933
Non- accrual Loans	17,237	27,644
90 Days Past Due Loans, Still Accruing Interest	3,166	597
Total Corporate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	5,754,921	5,687,142
30-89 Days Past Due	24,084	30,452
90 Days or More Past Due	22,806	29,144
Total Past Due	46,890	59,596
Total Loans	5,801,811	5,746,738
Non- accrual Loans	23,787	50,697
90 Days Past Due Loans, Still Accruing Interest	4,066	802
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	640,783	535,587
30-89 Days Past Due	3,464	3,216
90 Days or More Past Due	2,976	4,382
Total Past Due	6,440	7,598
Total Loans	647,223	543,185
Non- accrual Loans	5,201	6,290
90 Days Past Due Loans, Still Accruing Interest	214	145
1-4 family mortgage loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	290,066	287,892
30-89 Days Past Due	2,643	2,246
90 Days or More Past Due	1,552	1,325
Total Past Due	4,195	3,571
Total Loans	294,261	291,463
Non- accrual Loans	3,320	2,941
90 Days Past Due Loans, Still Accruing Interest	152	166
Installment Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	130,292	75,428
30-89 Days Past Due	766	506
90 Days or More Past Due	127	98
Total Past Due	893	604
Total Loans	131,185	76,032
Non- accrual Loans	0	43
90 Days Past Due Loans, Still Accruing Interest	127	60
Total Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,061,141	898,907
30-89 Days Past Due	6,873	5,968
90 Days or More Past Due	4,655	5,805
Total Past Due	11,528	11,773
Total Loans	1,072,669	910,680
Non- accrual Loans	8,521	9,274
90 Days Past Due Loans, Still Accruing Interest	493	371
Total Loans Excluding Covered Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	6,816,062	6,586,049
30-89 Days Past Due	30,957	36,420
90 Days or More Past Due	27,461	34,949
Total Past Due	58,418	71,369
Total Loans	6,874,480	6,657,418
Non- accrual Loans	32,308	59,971
90 Days Past Due Loans, Still Accruing Interest	4,559	1,173
Covered Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	48,743	66,331
30-89 Days Past Due	250	2,714
90 Days or More Past Due	2,226	10,390
Total Past Due	2,476	13,104
Total Loans	51,219	79,435
Non- accrual Loans	1,303	6,186
90 Days Past Due Loans, Still Accruing Interest	1,372	5,002
Loans Total
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	6,864,805	6,652,380
30-89 Days Past Due	31,207	39,134
90 Days or More Past Due	29,687	45,339
Total Past Due	60,894	84,473
Total Loans	6,925,699	6,736,853
Non- accrual Loans	33,611	66,157
90 Days Past Due Loans, Still Accruing Interest	$ 5,931	$ 6,175