Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRS - Aging Analysis of Past Due Loans and Non-Performing Loans by Class (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	$ 10,804,291	$ 10,365,369
Total Past Due		87,274	72,443
Total Loans		10,891,565	10,437,812
Non- accrual	[2]	53,475	66,924
90 Days or More Past Due, Still Accruing Interest		7,954	3,555
Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI	[3]	112,356	137,453
Receivables acquired with deteriorated credit quality | Non-accrual
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		748	763
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		44,160	52,570
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		43,114	19,873
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans		4,277,242	3,960,800
Commercial and industrial | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		4,764	12,702
Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	3,807,618	3,490,783
Total Past Due		36,449	39,131
Total Loans		3,844,067	3,529,914
Non- accrual	[2]	22,672	40,580
90 Days or More Past Due, Still Accruing Interest		1,544	1,830
Commercial and industrial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	427,295	430,221
Total Past Due		5,880	665
Total Loans		433,175	430,886
Non- accrual	[2]	2,992	219
90 Days or More Past Due, Still Accruing Interest		1,418	177
Commercial and industrial | 30-89 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		18,230	34,620
Commercial and industrial | 30-89 Days Past Due | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,477	280
Commercial and industrial | 90 Days or More Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		18,219	4,511
Commercial and industrial | 90 Days or More Past Due | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		4,403	385
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	4,477,065	4,534,968
Total Past Due		31,941	18,650
Total Loans		4,509,006	4,553,618
Non- accrual	[2]	18,054	15,767
90 Days or More Past Due, Still Accruing Interest		4,505	1,053
Commercial real estate | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		87,353	102,813
Commercial real estate | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	1,820,408	1,970,564
Total Past Due		14,510	9,256
Total Loans		1,834,918	1,979,820
Non- accrual	[2]	9,007	11,560
90 Days or More Past Due, Still Accruing Interest		1,402	345
Commercial real estate | Office, retail, and industrial | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		11,947	14,575
Commercial real estate | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	696,920	672,098
Total Past Due		6,171	3,365
Total Loans		703,091	675,463
Non- accrual	[2]	3,551	377
90 Days or More Past Due, Still Accruing Interest		2,269	20
Commercial real estate | Multi-family | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		13,014	14,071
Commercial real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	633,043	539,043
Total Past Due		558	777
Total Loans		633,601	539,820
Non- accrual	[2]	208	209
90 Days or More Past Due, Still Accruing Interest		243	371
Commercial real estate | Construction | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		4,952	8,843
Commercial real estate | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	1,326,694	1,353,263
Total Past Due		10,702	5,252
Total Loans		1,337,396	1,358,515
Non- accrual	[2]	5,288	3,621
90 Days or More Past Due, Still Accruing Interest		591	317
Commercial real estate | Other commercial real estate | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		57,440	65,324
Commercial real estate | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		15,643	9,016
Commercial real estate | 30-89 Days Past Due | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		5,366	3,156
Commercial real estate | 30-89 Days Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		3,530	3,117
Commercial real estate | 30-89 Days Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		107	198
Commercial real estate | 30-89 Days Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		6,640	2,545
Commercial real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		16,298	9,634
Commercial real estate | 90 Days or More Past Due | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		9,144	6,100
Commercial real estate | 90 Days or More Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		2,641	248
Commercial real estate | 90 Days or More Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		451	579
Commercial real estate | 90 Days or More Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		4,062	2,707
Total corporate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	8,711,978	8,455,972
Total Past Due		74,270	58,446
Total Loans		8,786,248	8,514,418
Non- accrual	[2]	43,718	56,566
90 Days or More Past Due, Still Accruing Interest		7,467	3,060
Total corporate loans | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		92,117	115,515
Total corporate loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		35,350	43,916
Total corporate loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		38,920	14,530
Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	2,092,313	1,909,397
Total Past Due		13,004	13,997
Total Loans		2,105,317	1,923,394
Non- accrual	[2]	9,757	10,358
90 Days or More Past Due, Still Accruing Interest		487	495
Consumer loans | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		20,239	21,938
Consumer loans | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	842,257	820,099
Total Past Due		5,646	6,956
Total Loans		847,903	827,055
Non- accrual	[2]	5,399	5,946
90 Days or More Past Due, Still Accruing Interest		0	98
Consumer loans | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	876,045	770,120
Total Past Due		4,136	4,237
Total Loans		880,181	774,357
Non- accrual	[2]	4,358	4,412
90 Days or More Past Due, Still Accruing Interest		41	0
Consumer loans | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	374,011	319,178
Total Past Due		3,222	2,804
Total Loans		377,233	321,982
Non- accrual	[2]	0	0
90 Days or More Past Due, Still Accruing Interest		446	397
Consumer loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		8,810	8,654
Consumer loans | 30-89 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		4,048	4,102
Consumer loans | 30-89 Days Past Due | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,986	2,145
Consumer loans | 30-89 Days Past Due | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		2,776	2,407
Consumer loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		4,194	5,343
Consumer loans | 90 Days or More Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,598	2,854
Consumer loans | 90 Days or More Past Due | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		2,150	2,092
Consumer loans | 90 Days or More Past Due | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		$ 446	$ 397

[1] PCI loans with an accretable yield are considered current.

[2] Includes PCI loans of $748,000 and $763,000 as of June 30, 2018 and December 31, 2017, respectively, which no longer have an accretable yield as estimates of expected future cash flows have decreased since the acquisition due to credit deterioration.

[3] Included in loans in the Consolidated Statements of Condition.