Contract Assets and Liabilities - Summary of net asset position for contracts in process (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Contract Assets and Liabilities
Unbilled revenue	$ 150,485	$ 111,153
Deferred revenue	(75,641)	(57,051)
Net asset position for contracts in process	$ 74,844	$ 54,102

Amount received for services rendered and products shipped, but not yet billed, for non-contractual agreements due within one year or the normal operating cycle, if longer.

No definition available.

Name:	us-gaap_UnbilledReceivablesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant