Summary of Significant Accounting Policies Schedule of Error Corrections and Prior Period Adjustments (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cash and due from banks		$ 190,663				$ 199,693				$ 190,663	$ 199,693		$ 213,914		$ 205,921
Accrued interest receivable and other assets		294,462				343,856				294,462	343,856
Accrued expenses and other liabilities		223,712				233,581				223,712	233,581
Retained earnings		1,425,320				1,315,948				1,425,320	1,315,948
Debt issuance cost	[1]	(961)				(1,096)				(961)	(1,096)
Deposit service fees										140,685	135,057		103,431
Other income										38,591	23,326		18,917
Technology and equipment										79,882	80,813		61,993
Income tax expense		23,845	$ 24,445	$ 24,599	$ 23,434	23,627	$ 24,995	$ 20,426	$ 23,984	96,323	93,032		91,973
Net income		$ 57,660	$ 51,817	$ 50,603	$ 47,047	$ 51,812	$ 51,370	$ 52,043	$ 49,504	$ 207,127	$ 204,729		$ 199,726
Earnings per common share, Basic (in dollars per share)		$ 0.61	$ 0.54	$ 0.53	$ 0.49	$ 0.54	$ 0.54	$ 0.55	$ 0.52	$ 2.17	$ 2.15		$ 2.10
Earnings per common share, Diluted (in dollars per share)		$ 0.60	$ 0.54	$ 0.53	$ 0.49	$ 0.54	$ 0.53	$ 0.55	$ 0.51	$ 2.16	$ 2.13		$ 2.08
Net (increase) in accrued interest receivable and other assets										$ 50,737	$ (44,334)	[2]	$ (2,552)	[2]
Net increase in accrued expenses and other liabilities										(18,918)	33,478	[2]	6,601	[2]
Net increase in derivative contract assets net of liabilities										$ 27,929	(6,489)		(49,158)
Scenario, Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cash and due from banks						$ 251,258					251,258
Accrued interest receivable and other assets	[3]					328,993					328,993
Accrued expenses and other liabilities						267,576					267,576
Retained earnings						1,317,559					1,317,559
Deposit service fees											136,578
Other income											23,573
Technology and equipment											80,026
Income tax expense											93,976
Net income											$ 206,340
Earnings per common share, Basic (in dollars per share)											$ 2.17
Earnings per common share, Diluted (in dollars per share)											$ 2.15
Net (increase) in accrued interest receivable and other assets	[2]										$ (49,899)		(24,502)
Net increase in accrued expenses and other liabilities	[2]										35,336		$ 9,213
Restatement Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cash and due from banks						199,693					199,693
Accrued interest receivable and other assets	[3]					343,856					343,856
Accrued expenses and other liabilities						233,581					233,581
Retained earnings						$ 1,315,948					1,315,948
HSA Bank [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income											37,443
HSA Bank [Member] | Scenario, Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income											$ 39,173

[1] In accordance with the adoption of ASU No. 2015-03, Interest-Imputation of Interest (Subtopic 835-30) - Simplifying the Presentation of Debt Issuance Costs, debt issuance cost is accounted for as a reduction to long-term debt. Previously debt issuance cost was included in accrued interest receivable and other assets within the accompanying Consolidated Balance Sheets.

[2] An additional line item, net decrease (increase) in derivative contract assets net of liabilities, was added to the Consolidated Statements of Cash Flows to detail the net change in derivative balances subject to offsetting. The update removed $6.5 million and $49.2 million in net increases in derivative contract assets net of liabilities from the net (increase) in accrued interest receivable and other assets and net increase in accrued expenses and other liabilities line items for the years ended December 31, 2015 and December 31, 2014 respectively.

[3] The amount recorded as revised includes the impact of a $1.1 million reclassification of debt issuance cost from accrued interest receivable and other assets into long-term debt. The reclassification was made in accordance with the Company's adoption of ASU No. 2015-03, Interest-Imputation of Interest (Subtopic 835-30) - Simplifying the Presentation of Debt Issuance Costs, and is not considered part of the error correction.