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Loans Receivable - Changes in the Allowance for Losses on Loans Receivable (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jan. 01, 2020	Jan. 01, 2019
Allowance for loan losses
Cumulative effect of ASU 2016-13			$ 9,649	$ (1,570)
Changes in allowance for losses on allocated loans receivable
Beginning balance	$ 57,941	$ 55,214
Current period provision	27,637	6,467
Charge-offs	(5,266)	(7,405)
Recoveries	1,793	1,445
Ending balance	92,897	55,721
Loans classified as held-for-investment sold	50,000
Gain on sale of loans	1,302	0
Personal Banking
Changes in allowance for losses on allocated loans receivable
Beginning balance	18,356
Current period provision	10,666
Charge-offs	(4,120)
Recoveries	1,072
Ending balance	37,619
Personal Banking \| Residential mortgage loans
Changes in allowance for losses on allocated loans receivable
Beginning balance	2,574
Current period provision	894
Charge-offs	(343)
Recoveries	107
Ending balance	10,673
Personal Banking \| Home equity loans
Changes in allowance for losses on allocated loans receivable
Beginning balance	3,189
Current period provision	895
Charge-offs	(289)
Recoveries	205
Ending balance	9,786
Personal Banking \| Vehicle loans
Changes in allowance for losses on allocated loans receivable
Beginning balance	7,292
Current period provision	5,359
Charge-offs	(1,843)
Recoveries	344
Ending balance	11,994
Personal Banking \| Consumer loans
Changes in allowance for losses on allocated loans receivable
Beginning balance	5,301
Current period provision	3,518
Charge-offs	(1,645)
Recoveries	416
Ending balance	5,166
Commercial Banking
Changes in allowance for losses on allocated loans receivable
Beginning balance	39,585
Current period provision	16,971
Charge-offs	(1,146)
Recoveries	721
Ending balance	55,278
Commercial Banking \| Commercial real estate loans
Changes in allowance for losses on allocated loans receivable
Beginning balance	15,843
Current period provision	11,269
Charge-offs	(310)
Recoveries	290
Ending balance	29,380
Commercial Banking \| Commercial real estate loans - owner occupied
Changes in allowance for losses on allocated loans receivable
Beginning balance	5,745
Current period provision	1,365
Charge-offs	(21)
Recoveries	7
Ending balance	8,374
Commercial Banking \| Commercial loans
Changes in allowance for losses on allocated loans receivable
Beginning balance	17,997
Current period provision	4,337
Charge-offs	(815)
Recoveries	424
Ending balance	17,524
Off-Balance Sheet Exposure
Changes in allowance for losses on allocated loans receivable
Beginning balance	974
Current period provision	1,480
Charge-offs	0
Recoveries	0
Ending balance	4,704
Off-Balance Sheet Exposure \| Personal Banking
Changes in allowance for losses on allocated loans receivable
Beginning balance	725
Current period provision	4
Charge-offs	0
Recoveries	0
Ending balance	34
Off-Balance Sheet Exposure \| Personal Banking \| Home equity loans
Changes in allowance for losses on allocated loans receivable
Beginning balance	323
Current period provision	4
Charge-offs	0
Recoveries	0
Ending balance	34
Off-Balance Sheet Exposure \| Personal Banking \| Consumer loans
Changes in allowance for losses on allocated loans receivable
Beginning balance	402
Current period provision	0
Charge-offs	0
Recoveries	0
Ending balance	0
Off-Balance Sheet Exposure \| Commercial Banking
Changes in allowance for losses on allocated loans receivable
Beginning balance	249
Current period provision	1,476
Charge-offs	0
Recoveries	0
Ending balance	4,670
Off-Balance Sheet Exposure \| Commercial Banking \| Commercial real estate loans
Changes in allowance for losses on allocated loans receivable
Beginning balance	77
Current period provision	1,283
Charge-offs	0
Recoveries	0
Ending balance	3,294
Off-Balance Sheet Exposure \| Commercial Banking \| Commercial real estate loans - owner occupied
Changes in allowance for losses on allocated loans receivable
Beginning balance	3
Current period provision	4
Charge-offs	0
Recoveries	0
Ending balance	95
Off-Balance Sheet Exposure \| Commercial Banking \| Commercial loans
Changes in allowance for losses on allocated loans receivable
Beginning balance	169
Current period provision	189
Charge-offs	0
Recoveries	0
Ending balance	1,281
Originated
Changes in allowance for losses on allocated loans receivable
Beginning balance	51,439	51,751
Current period provision		3,383
Charge-offs		(4,475)
Recoveries		1,052
Ending balance	82,431	51,711
Originated \| Personal Banking
Changes in allowance for losses on allocated loans receivable
Beginning balance		18,318
Current period provision		2,973
Charge-offs		(3,449)
Recoveries		760
Ending balance		18,602
Originated \| Personal Banking \| Residential mortgage loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		4,054
Current period provision		186
Charge-offs		(349)
Recoveries		114
Ending balance		4,005
Originated \| Personal Banking \| Home equity loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		3,184
Current period provision		(35)
Charge-offs		(112)
Recoveries		25
Ending balance		3,062
Originated \| Personal Banking \| Consumer loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		11,080
Current period provision		2,822
Charge-offs		(2,988)
Recoveries		621
Ending balance		11,535
Originated \| Commercial Banking
Changes in allowance for losses on allocated loans receivable
Beginning balance		33,433
Current period provision		410
Charge-offs		(1,026)
Recoveries		292
Ending balance		33,109
Originated \| Commercial Banking \| Commercial real estate loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		26,379
Current period provision		(464)
Charge-offs		(569)
Recoveries		124
Ending balance		25,470
Originated \| Commercial Banking \| Commercial loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		7,054
Current period provision		874
Charge-offs		(457)
Recoveries		168
Ending balance		7,639
Acquired
Changes in allowance for losses on allocated loans receivable
Beginning balance	6,502	3,463
Current period provision		3,084
Charge-offs		(2,930)
Recoveries		393
Ending balance	10,466	4,010
Acquired \| Personal Banking
Changes in allowance for losses on allocated loans receivable
Beginning balance		850
Current period provision		87
Charge-offs		(82)
Recoveries		90
Ending balance		945
Acquired \| Personal Banking \| Residential mortgage loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		83
Current period provision		8
Charge-offs		(8)
Recoveries		9
Ending balance		92
Acquired \| Personal Banking \| Home equity loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		348
Current period provision		45
Charge-offs		(42)
Recoveries		48
Ending balance		399
Acquired \| Personal Banking \| Consumer loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		419
Current period provision		34
Charge-offs		(32)
Recoveries		33
Ending balance		454
Acquired \| Commercial Banking \| Residential mortgage loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		1,996
Current period provision		255
Charge-offs		(35)
Recoveries		251
Ending balance		2,467
Acquired \| Commercial Banking \| Home equity loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		617
Current period provision		2,742
Charge-offs		(2,813)
Recoveries		52
Ending balance		598
Acquired \| Commercial Banking \| Consumer loans
Changes in allowance for losses on allocated loans receivable
Beginning balance		2,613
Current period provision		2,997
Charge-offs		(2,848)
Recoveries		303
Ending balance		$ 3,065
Accounting Standards Update 2016-13
Allowance for loan losses
Cumulative effect of ASU 2016-13			10,792
Changes in allowance for losses on allocated loans receivable
Initial allowance on PCD loans	$ 517
Accounting Standards Update 2016-13 \| Personal Banking
Allowance for loan losses
Cumulative effect of ASU 2016-13			11,645
Accounting Standards Update 2016-13 \| Personal Banking \| Residential mortgage loans
Allowance for loan losses
Cumulative effect of ASU 2016-13			7,441
Accounting Standards Update 2016-13 \| Personal Banking \| Home equity loans
Allowance for loan losses
Cumulative effect of ASU 2016-13			5,786
Accounting Standards Update 2016-13 \| Personal Banking \| Vehicle loans
Allowance for loan losses
Cumulative effect of ASU 2016-13			842
Accounting Standards Update 2016-13 \| Personal Banking \| Consumer loans
Allowance for loan losses
Cumulative effect of ASU 2016-13			(2,424)
Accounting Standards Update 2016-13 \| Commercial Banking
Allowance for loan losses
Cumulative effect of ASU 2016-13			(853)
Accounting Standards Update 2016-13 \| Commercial Banking \| Commercial real estate loans
Allowance for loan losses
Cumulative effect of ASU 2016-13			2,288
Accounting Standards Update 2016-13 \| Commercial Banking \| Commercial real estate loans - owner occupied
Allowance for loan losses
Cumulative effect of ASU 2016-13			1,278
Accounting Standards Update 2016-13 \| Commercial Banking \| Commercial loans
Allowance for loan losses
Cumulative effect of ASU 2016-13			(4,419)
Accounting Standards Update 2016-13 \| Off-Balance Sheet Exposure
Allowance for loan losses
Cumulative effect of ASU 2016-13			2,250
Accounting Standards Update 2016-13 \| Off-Balance Sheet Exposure \| Personal Banking
Allowance for loan losses
Cumulative effect of ASU 2016-13			(695)
Accounting Standards Update 2016-13 \| Off-Balance Sheet Exposure \| Personal Banking \| Home equity loans
Allowance for loan losses
Cumulative effect of ASU 2016-13			(293)
Accounting Standards Update 2016-13 \| Off-Balance Sheet Exposure \| Personal Banking \| Consumer loans
Allowance for loan losses
Cumulative effect of ASU 2016-13			(402)
Accounting Standards Update 2016-13 \| Off-Balance Sheet Exposure \| Commercial Banking
Allowance for loan losses
Cumulative effect of ASU 2016-13			2,945
Accounting Standards Update 2016-13 \| Off-Balance Sheet Exposure \| Commercial Banking \| Commercial real estate loans
Allowance for loan losses
Cumulative effect of ASU 2016-13			1,934
Accounting Standards Update 2016-13 \| Off-Balance Sheet Exposure \| Commercial Banking \| Commercial real estate loans - owner occupied
Allowance for loan losses
Cumulative effect of ASU 2016-13			88
Accounting Standards Update 2016-13 \| Off-Balance Sheet Exposure \| Commercial Banking \| Commercial loans
Allowance for loan losses
Cumulative effect of ASU 2016-13			$ 923