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	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 7,926,386	$ 7,119,965
Total Past Due	53,151	41,750
Total Loans	7,979,537	7,161,715
Non- accrual	37,312	29,430
90 Days or More Past Due, Still Accruing Interest	5,406	3,057
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,684,411	2,516,197
Total Past Due	15,331	8,529
Total Loans	2,699,742	2,524,726
Non- accrual	6,303	5,587
90 Days or More Past Due, Still Accruing Interest	1,050	857
Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	401,242	387,109
Total Past Due	616	331
Total Loans	401,858	387,440
Non- accrual	475	355
90 Days or More Past Due, Still Accruing Interest	0	0
Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,516,265	1,386,383
Total Past Due	13,410	9,071
Total Loans	1,529,675	1,395,454
Non- accrual	16,815	6,875
90 Days or More Past Due, Still Accruing Interest	34	4
Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	584,040	526,625
Total Past Due	3,064	1,699
Total Loans	587,104	528,324
Non- accrual	321	796
90 Days or More Past Due, Still Accruing Interest	354	548
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	370,596	216,377
Total Past Due	420	505
Total Loans	371,016	216,882
Non- accrual	360	905
90 Days or More Past Due, Still Accruing Interest	20	0
Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	992,309	922,531
Total Past Due	8,346	8,659
Total Loans	1,000,655	931,190
Non- accrual	4,797	5,611
90 Days or More Past Due, Still Accruing Interest	2,925	661
Total commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,463,210	3,051,916
Total Past Due	25,240	19,934
Total Loans	3,488,450	3,071,850
Non- accrual	22,293	14,187
90 Days or More Past Due, Still Accruing Interest	3,333	1,213
Total corporate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	6,548,863	5,955,222
Total Past Due	41,187	28,794
Total Loans	6,590,050	5,984,016
Non- accrual	29,071	20,129
90 Days or More Past Due, Still Accruing Interest	4,383	2,070
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	717,461	647,175
Total Past Due	5,420	6,293
Total Loans	722,881	653,468
Non- accrual	4,527	5,310
90 Days or More Past Due, Still Accruing Interest	153	216
1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	411,585	350,980
Total Past Due	3,996	4,874
Total Loans	415,581	355,854
Non- accrual	3,261	3,416
90 Days or More Past Due, Still Accruing Interest	604	528
Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	222,273	136,780
Total Past Due	1,572	822
Total Loans	223,845	137,602
Non- accrual	0	20
90 Days or More Past Due, Still Accruing Interest	266	69
Total consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,351,319	1,134,935
Total Past Due	10,988	11,989
Total Loans	1,362,307	1,146,924
Non- accrual	7,788	8,746
90 Days or More Past Due, Still Accruing Interest	1,023	813
Covered loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	26,204	29,808
Total Past Due	976	967
Total Loans	27,180	30,775
Non- accrual	453	555
90 Days or More Past Due, Still Accruing Interest	0	174
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	27,927	19,049
30-89 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,162	4,956
30-89 Days Past Due | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	383	245
30-89 Days Past Due | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,677	2,647
30-89 Days Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,566	541
30-89 Days Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	47	0
30-89 Days Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,926	3,575
30-89 Days Past Due | Total commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,216	6,763
30-89 Days Past Due | Total corporate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	20,761	11,964
30-89 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,278	3,247
30-89 Days Past Due | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,901	2,680
30-89 Days Past Due | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,306	753
30-89 Days Past Due | Total consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,485	6,680
30-89 Days Past Due | Covered loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	681	405
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	25,224	22,701
90 Days or More Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,169	3,573
90 Days or More Past Due | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	233	86
90 Days or More Past Due | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,733	6,424
90 Days or More Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	498	1,158
90 Days or More Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	373	505
90 Days or More Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,420	5,084
90 Days or More Past Due | Total commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	15,024	13,171
90 Days or More Past Due | Total corporate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	20,426	16,830
90 Days or More Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,142	3,046
90 Days or More Past Due | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,095	2,194
90 Days or More Past Due | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	266	69
90 Days or More Past Due | Total consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,503	5,309
90 Days or More Past Due | Covered loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 295	$ 562