Basis of Presentation (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) reporting_unit segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018	Jun. 30, 2020 USD ($)	Jan. 01, 2020 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of reportable segments (in segments) | segment			5
Premium receivable, allowance for credit loss	$ 6,616		$ 6,616		$ 1,590		$ 6,627
Number of reporting units | reporting_unit			3
Goodwill impairment	161,115	$ 0	$ 161,115	$ 0
Retained earnings (accumulated deficit)	$ 1,289,552		$ 1,289,552		$ 1,505,738
Accounting standards update [extensible list]			us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201807Member
Percent of investments with exposure to LIBOR	6.00%		6.00%
Investments with exposure to LIBOR	$ 188,000		$ 188,000
Investments with exposure to LIBOR, issued in 2020 or 2019					31.00%
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premium receivable, allowance for credit loss					$ 5,160
Retained earnings (accumulated deficit)								$ (4,100)