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		Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	$ 11,357,176	$ 10,365,369
Past Due		89,607	72,443
Total loans		11,446,783	10,437,812
Non-accrual	[2]	56,935	66,924
90 Days or More Past Due, Still Accruing Interest		8,282	3,555
Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		113,868	137,453
Receivables acquired with deteriorated credit quality | Non-accrual
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		58	763
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		40,102	52,570
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		49,505	19,873
Commercial, industrial, and agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		4,551,221	3,960,800
Commercial, industrial, and agricultural | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		4,457	12,702
Commercial, industrial, and agricultural | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	4,085,164	3,490,783
Past Due		35,129	39,131
Total loans		4,120,293	3,529,914
Non-accrual	[2]	33,507	40,580
90 Days or More Past Due, Still Accruing Interest		422	1,830
Commercial, industrial, and agricultural | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	428,357	430,221
Past Due		2,571	665
Total loans		430,928	430,886
Non-accrual	[2]	1,564	219
90 Days or More Past Due, Still Accruing Interest		101	177
Commercial, industrial, and agricultural | 30-89 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		8,832	34,620
Commercial, industrial, and agricultural | 30-89 Days Past Due | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		940	280
Commercial, industrial, and agricultural | 90 Days or More Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		26,297	4,511
Commercial, industrial, and agricultural | 90 Days or More Past Due | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		1,631	385
Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	4,561,677	4,534,968
Past Due		34,572	18,650
Total loans		4,596,249	4,553,618
Non-accrual	[2]	12,615	15,767
90 Days or More Past Due, Still Accruing Interest		6,467	1,053
Commercial real estate loans | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		89,878	102,813
Commercial real estate loans | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	1,803,059	1,970,564
Past Due		17,858	9,256
Total loans		1,820,917	1,979,820
Non-accrual	[2]	6,510	11,560
90 Days or More Past Due, Still Accruing Interest		4,081	345
Commercial real estate loans | Office, retail, and industrial | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		16,556	14,575
Commercial real estate loans | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	759,402	672,098
Past Due		4,783	3,365
Total loans		764,185	675,463
Non-accrual	[2]	3,107	377
90 Days or More Past Due, Still Accruing Interest		189	20
Commercial real estate loans | Multi-family | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		13,663	14,071
Commercial real estate loans | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	645,774	539,043
Past Due		3,563	777
Total loans		649,337	539,820
Non-accrual	[2]	144	209
90 Days or More Past Due, Still Accruing Interest		0	371
Commercial real estate loans | Construction | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		4,838	8,843
Commercial real estate loans | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	1,353,442	1,353,263
Past Due		8,368	5,252
Total loans		1,361,810	1,358,515
Non-accrual	[2]	2,854	3,621
90 Days or More Past Due, Still Accruing Interest		2,197	317
Commercial real estate loans | Other commercial real estate | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		54,821	65,324
Commercial real estate loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		18,036	9,016
Commercial real estate loans | 30-89 Days Past Due | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		8,209	3,156
Commercial real estate loans | 30-89 Days Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		1,487	3,117
Commercial real estate loans | 30-89 Days Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		3,419	198
Commercial real estate loans | 30-89 Days Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		4,921	2,545
Commercial real estate loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		16,536	9,634
Commercial real estate loans | 90 Days or More Past Due | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		9,649	6,100
Commercial real estate loans | 90 Days or More Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		3,296	248
Commercial real estate loans | 90 Days or More Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		144	579
Commercial real estate loans | 90 Days or More Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		3,447	2,707
Total corporate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	9,075,198	8,455,972
Past Due		72,272	58,446
Total loans		9,147,470	8,514,418
Non-accrual	[2]	47,686	56,566
90 Days or More Past Due, Still Accruing Interest		6,990	3,060
Total corporate loans | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		94,335	115,515
Total corporate loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		27,808	43,916
Total corporate loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		44,464	14,530
Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	2,281,978	1,909,397
Past Due		17,335	13,997
Total loans		2,299,313	1,923,394
Non-accrual	[2]	9,249	10,358
90 Days or More Past Due, Still Accruing Interest		1,292	495
Consumer loans | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		19,533	21,938
Consumer loans | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	843,217	820,099
Past Due		8,390	6,956
Total loans		851,607	827,055
Non-accrual	[2]	5,393	5,946
90 Days or More Past Due, Still Accruing Interest		104	98
Consumer loans | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	1,009,925	770,120
Past Due		7,256	4,237
Total loans		1,017,181	774,357
Non-accrual	[2]	3,856	4,412
90 Days or More Past Due, Still Accruing Interest		1,147	0
Consumer loans | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	428,836	319,178
Past Due		1,689	2,804
Total loans		430,525	321,982
Non-accrual	[2]	0	0
90 Days or More Past Due, Still Accruing Interest		41	397
Consumer loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		12,294	8,654
Consumer loans | 30-89 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		6,285	4,102
Consumer loans | 30-89 Days Past Due | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		4,361	2,145
Consumer loans | 30-89 Days Past Due | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		1,648	2,407
Consumer loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		5,041	5,343
Consumer loans | 90 Days or More Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		2,105	2,854
Consumer loans | 90 Days or More Past Due | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		2,895	2,092
Consumer loans | 90 Days or More Past Due | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		$ 41	$ 397

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

[2] Includes PCI loans of $58,000 and $763,000 as of December 31, 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.