Basis of Presentation - Allowance for Credit Losses: Loans (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) class_financing_receivable portfolio_segment	Dec. 31, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of portfolio segments | portfolio_segment	6
Number of classes of financing receivables | class_financing_receivable	10
Forecast period for estimated credit loss for loans	3 years
Lower Limit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sponsor equity contribution, percentage of acquisition price	50.00%
Mid stage | Upper Limit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue threshold of portfolio segment subcategories	$ 15.0
Investor dependent | Early stage
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue threshold of portfolio segment subcategories	5.0
Investor dependent | Mid stage | Lower Limit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue threshold of portfolio segment subcategories	5.0
Investor dependent | Later stage
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue threshold of portfolio segment subcategories	15.0
Accrued interest receivable and other assets | Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued interest receivable	$ 111.8	$ 119.1