Revenue (Contract Assets and Advance Billings) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contracts assets, current	$ 17,050	$ 16,115
Contracts assets, noncurrent	10,050	13,092
Advance billings, current	200,224	215,790
Advance billings, noncurrent	12,832	$ 12,778
Increase (Decrease)
Contracts assets, current	935
Contracts assets, noncurrent	(3,042)
Advance billings, current	(15,566)
Advance billings, noncurrent	$ 54