Summary of Significant Accounting Policies - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Contract Assets
Balance at beginning of period	$ 2,736	$ 10,213	$ 10,213
Change due to acquisitions / disposals	7,469		6,573
Change related to credit allowance	(79)
Other changes in the period	15,256		(14,050)
Balance at end of period	25,382		2,736
Contract Liabilities
Balance at beginning of period	166,918	130,986	130,986
Change due to acquisitions / disposals	37,047		31,556
Other changes in the period	13,489		4,376
Balance at end of period	217,454		$ 166,918
Revenue related to our contract liabilities	$ 164,400
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Contract Liabilities
Revenue related to our contract liabilities		$ 123,300