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, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer, Excluding Assessed Tax	$ 208,293	$ 200,673			$ 185,945
Noninterest Income	285,315	282,568	$ 285,315	$ 282,568	259,478
Deposit Service Fees [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	168,022	162,183			151,137
Investment Advisory, Management and Administrative Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	32,932	32,843			31,055
Other Non Interest Income [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	7,339	5,647			3,753
Non-Interest Income Within the Scope of Other GAAP Topics [Member]
Noninterest Income	77,022	81,895			73,533
Operating Segments [Member] | Commercial Banking [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	22,466	22,920			22,020
Noninterest Income	59,063	64,765	59,063	64,765	55,194
Operating Segments [Member] | Commercial Banking [Member] | Deposit Service Fees [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	12,136	12,775			12,203
Operating Segments [Member] | Commercial Banking [Member] | Investment Advisory, Management and Administrative Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	10,330	10,145			9,817
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	36,597	41,845			33,174
Operating Segments [Member] | Community Banking [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	88,603	88,387			86,291
Noninterest Income	109,270	109,669	109,270	109,669	107,368
Operating Segments [Member] | Community Banking [Member] | Deposit Service Fees [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	63,572	63,522			64,194
Operating Segments [Member] | Community Banking [Member] | Investment Advisory, Management and Administrative Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	22,637	22,732			21,274
Operating Segments [Member] | Community Banking [Member] | Other Non Interest Income [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	2,394	2,133			823
Operating Segments [Member] | Community Banking [Member] | Non-Interest Income Within the Scope of Other GAAP Topics [Member]
Noninterest Income	20,667	21,282			21,077
Operating Segments [Member] | HSA Bank [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	97,041	89,323			77,378
Noninterest Income	97,041	89,323	97,041	89,323	77,378
Operating Segments [Member] | HSA Bank [Member] | Deposit Service Fees [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	92,096	85,809			74,448
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	4,945	3,514			2,930
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	183	43			256
Noninterest Income	19,941	18,811	$ 19,941	$ 18,811	19,538
Corporate, Non-Segment [Member] | Deposit Service Fees [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	218	77			292
Corporate, Non-Segment [Member] | Investment Advisory, Management and Administrative Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	(35)	(34)			(36)
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	$ 19,758	$ 18,768			$ 19,282