Revenues, net - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017		Dec. 31, 2016	[2]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact on adoption of accounting standard update			$ 454,000	[1]	$ 1,453,000
Accounts receivable not billed	$ 63,952,000		49,125,000
Contract liability, revenue recognized	9,147,000
Capitalized contract cost, net	713,000
Increase in capitalized contract costs	567,000
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact on adoption of accounting standard update			454,000	[1]	$ (4,546,000)
Impact of adoption of Topic 606 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact on adoption of accounting standard update			454,000
Contract Acquisition Costs
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Capitalized contract acquisition costs		$ 454,000
Capitalized contract acquisition costs, amount amortized	308,000
Impairment loss in relation to costs capitalized	0
Contract Fulfillment Costs
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Capitalized contract cost, net	4,051,000		$ 2,769,000
Increase in capitalized contract costs	2,216,000
Capitalized contract acquisition costs, amount amortized	934,000
Impairment loss in relation to costs capitalized	$ 0

[1] Refer to Note 2(d) to the consolidated financial statements for details.

[2] Refer to Note 2(p) to the consolidated financial statements for details.