General - Accounts Receivable, Contract Assets and Contract Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Operating results by business segment
Accounts receivable	$ 854,715	$ 854,715	$ 786,395
Change in accounts receivable (in dollars)		$ 68,320
Change in accounts receivable (as a percent)		8.70%
Contract assets	12,891	$ 12,891	4,647
Change in contract assets (in dollars)		$ 8,244
Change in contract assets (as a percent)		177.40%
Contract liabilities - current	7,809	$ 7,809	16,853
Change in contract liabilities - current (in dollars)		$ (9,044)
Change in contract liabilities - current (as a percent)		(53.70%)
Contract liabilities - long-term	12,187	$ 12,187	$ 13,441
Change in contract liabilities - long-term (in dollars)		$ (1,254)
Change in contract liabilities - long-term (as a percent)		(9.30%)
Revenue recognized previously included in current contract liabilities	$ 2,600	$ 14,200