Summary of Significant Accounting Policies - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Contract Assets
Balance at beginning of period	$ 10,213	$ 30,116	$ 30,116
Change due to acquisitions	6,953		2,833
Change due to conditional versus unconditional	8,945		(6,244)
Reclassified to unbilled accounts receivable			(28,980)
Balance at end of period	8,221		10,213
Contract Liabilities
Balance at beginning of period	130,986	106,005	106,005
Change due to acquisitions	31,604		8,195
Change in timing for performance obligation to be satisfied	2,699		16,786
Balance at end of period	165,289		$ 130,986
Increase (Decrease) In Income Taxes Abstract
Revenue related to our contract liabilities	109,700
Impairment losses	$ 0	0
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Increase (Decrease) In Income Taxes Abstract
Revenue related to our contract liabilities		$ 94,200