Contract Assets and Contract Liabilities (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Contract Assets
Balance at beginning of year	$ 366,168
Recognized in current year	242,020
Reclassified to accounts receivable	(223,148)
Foreign currency impact	(6,956)
Balance at end of period	378,084
Contract Liabilities
Balance at beginning of year	463,704
Recognized in current year	120,500
Amounts in beginning balance reclassified to revenue	(92,137)
Current year amounts reclassified to revenue	(10,584)
Foreign currency impact	(10,157)
Balance at end of period	$ 471,326