Revenue from Contracts with Customers - Contract Balances (Details) - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Contract with Customer [Line Items]
Contract assets	$ 1,228,000		$ 2,362,000
Deferred revenue and customer advances	5,229,000		6,034,000
Revenues recognized from satisfied in previous period	0	$ 700,000
Capitalized contract costs	2,300,000
Impairment	0
Other long-term liabilities
Contract with Customer [Line Items]
Deferred revenue, included in other long-term liabilities	$ 965,000		$ 578,000