Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
VIEs carrying value	$ 6,327,268	$ 4,654,803
Liabilities	4,904,166	3,305,593
Variable Interest Entity, Primary Beneficiary | PPM RRG
Variable Interest Entity [Line Items]
VIEs carrying value	145,000
Surplus Notes	5,000
Liabilities	145,000
Equity investments | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
VIEs carrying value	$ 284,700	$ 282,200