Accounting Policies (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Accounts Receivable, Allowance for Credit Loss				$ 2,300	$ 7,500
Interest Receivable	$ 1,600
Financing Receivable, Allowance for Credit Loss [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	559,419	$ 625,409	$ 636,659		1,075,409	$ 1,303,079	$ 1,359,033	$ 1,391,500	$ (5,900)	$ 1,415,298
Interest Receivable	1,600
Accounts Receivable, Allowance for Credit Loss				$ 2,300	$ 7,500
Accounts Receivable [Member]
Accounting Policies [Abstract]
Financing Receivable, Allowance for Credit Loss	9,200
Financing Receivable, Allowance for Credit Loss, Writeoff	5,300
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	$ 5,300