Summary of Significant Accounting Policies - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 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 due to conditional versus unconditional	13,389		(14,050)
Change related to credit allowance	(79)
Balance at end of period	23,515		2,736
Contract Liabilities
Balance at beginning of period	166,918	130,986	130,986
Change due to acquisitions / disposals	37,047		31,556
Change in timing for performance obligation to be satisfied	22,082		4,376
Balance at end of period	226,047		$ 166,918
Revenue related to our contract liabilities	$ 152,400
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Contract Liabilities
Revenue related to our contract liabilities		$ 109,700