Revenue from contracts with Customers Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from Contract with Customer, Excluding Assessed Tax	$ 198,737	$ 208,293			$ 200,673
Noninterest Income	285,277	285,315	$ 285,277	$ 285,315	282,568
Deposit Service Fees [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	156,032	168,022			162,183
Investment Advisory, Management and Administrative Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	32,916	32,932			32,843
Other Non Interest Income [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	9,789	7,339			5,647
Non-Interest Income Within the Scope of Other GAAP Topics [Member]
Noninterest Income	86,540	77,022			81,895
Operating Segments [Member] | Commercial Banking [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	22,278	22,466			22,920
Noninterest Income	58,366	59,063	58,366	59,063	64,765
Operating Segments [Member] | Commercial Banking [Member] | Deposit Service Fees [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	11,634	12,136			12,775
Operating Segments [Member] | Commercial Banking [Member] | Investment Advisory, Management and Administrative Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	10,644	10,330			10,145
Operating Segments [Member] | Commercial Banking [Member] | Other Non Interest Income [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0	0			0
Operating Segments [Member] | Commercial Banking [Member] | Non-Interest Income Within the Scope of Other GAAP Topics [Member]
Noninterest Income	36,088	36,597			41,845
Operating Segments [Member] | Community Banking [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	75,562	88,603			88,387
Noninterest Income	106,279	109,270	106,279	109,270	109,669
Operating Segments [Member] | Community Banking [Member] | Deposit Service Fees [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	51,599	63,572			63,522
Operating Segments [Member] | Community Banking [Member] | Investment Advisory, Management and Administrative Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	22,307	22,637			22,732
Operating Segments [Member] | Community Banking [Member] | Other Non Interest Income [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	1,656	2,394			2,133
Operating Segments [Member] | Community Banking [Member] | Non-Interest Income Within the Scope of Other GAAP Topics [Member]
Noninterest Income	30,717	20,667			21,282
Operating Segments [Member] | HSA Bank [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	100,826	97,041			89,323
Noninterest Income	100,826	97,041	100,826	97,041	89,323
Operating Segments [Member] | HSA Bank [Member] | Deposit Service Fees [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	92,693	92,096			85,809
Operating Segments [Member] | HSA Bank [Member] | Investment Advisory, Management and Administrative Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0	0			0
Operating Segments [Member] | HSA Bank [Member] | Other Non Interest Income [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	8,133	4,945			3,514
Operating Segments [Member] | HSA Bank [Member] | Non-Interest Income Within the Scope of Other GAAP Topics [Member]
Noninterest Income	0	0			0
Corporate, Non-Segment [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	71	183			43
Noninterest Income	19,806	19,941	$ 19,806	$ 19,941	18,811
Corporate, Non-Segment [Member] | Deposit Service Fees [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	106	218			77
Corporate, Non-Segment [Member] | Investment Advisory, Management and Administrative Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	(35)	(35)			(34)
Corporate, Non-Segment [Member] | Other Non Interest Income [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0	0			0
Corporate, Non-Segment [Member] | Non-Interest Income Within the Scope of Other GAAP Topics [Member]
Noninterest Income	$ 19,735	$ 19,758			$ 18,768