Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands		12 Months Ended
	May 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosures [Line Items]
Current Federal Tax Expense (Benefit)		$ 9,424	$ 10,382	$ 1,127
Current State and Local Tax Expense (Benefit)		164	263	17
Deferred Federal Income Tax Expense (Benefit)		7,357	19,451	254,420
Deferred State and Local Income Tax Expense (Benefit)		128	(4)	(421)
Total income tax expense		17,073	30,092	255,143
Subsidiaries [Member]
Income Tax Disclosures [Line Items]
Current Federal Tax Expense (Benefit)		18,093	19,283	1,127
Current State and Local Tax Expense (Benefit)		570	438	17
Deferred Federal Income Tax Expense (Benefit)		20,485	30,979	210,842
Deferred State and Local Income Tax Expense (Benefit)		0	0	0
Total income tax expense	$ 34,600	$ 39,148	$ 50,700	$ 211,986