Interest Expense (Details) - USD ($)		1 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended
	Dec. 22, 2020	Feb. 28, 2021	Dec. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Interest and Debt Expense [Abstract]
Interest Expense, Debt				$ 13,526,000	$ 20,893,000		$ 44,476,000	$ 64,285,000
Accretion of fair value adjustment on Senior Notes				815,000	549,000		2,658,000	1,647,000
Amortization of Debt Issuance Costs				1,707,000	1,032,000		7,075,000	3,094,000
Interest Expense, Total				16,048,000	22,474,000		54,209,000	69,026,000
Debt Instrument [Line Items]
Subordinated Borrowing, Interest Rate	4.625%
Repayments of Secured Debt							300,000,000	249,214,000
Amortization of Debt Issuance Costs				1,707,000	$ 1,032,000		7,075,000	$ 3,094,000
Term Loan Facility
Debt Instrument [Line Items]
Payments of Debt Restructuring Costs							$ 1,600,000
2018 Credit Agreement
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate During Period						4.50%	3.50%
2018 Credit Agreement | Term Loan Facility
Interest and Debt Expense [Abstract]
Amortization of Debt Issuance Costs		$ 900,000		500,000			$ 1,800,000
Debt Instrument [Line Items]
Repayments of Secured Debt			$ 500,000,000	100,000,000			300,000,000
Accretion Expense				900,000			2,900,000
Amortization of Debt Issuance Costs		$ 900,000		$ 500,000			$ 1,800,000