Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
VIEs carrying value	$ 6,358,187	$ 4,654,803
Liabilities	4,934,147	3,305,593
Variable Interest Entity, Primary Beneficiary | PPM RRG
Variable Interest Entity [Line Items]
VIEs carrying value	146,000
Surplus Notes	5,000
Liabilities	146,000
Equity investments | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
VIEs carrying value	$ 282,300	$ 282,200