Significant Accounting Policies - Assessment of Revenue under ASC 606 (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred Cost of Sales, After Transition Adjustment	$ 2,412	$ 4,300
Contract where payment had not been received, collection no longer reasonably assured	10,300
Write-off of deferred cost of sales	1,400
Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Amounts Invoiced and Not Collected, Prior to Transition Adjustment	48,883
Amounts Invoiced and Not Collected, Transition Adjustment	(21,385)
Amounts Invoiced and Not Collected, Write-off of Customer Contracts where Collection is no Longer Reasonable Assured	(10,273)
Amounts Invoiced and Not Collected, After Transition Adjustment	17,225
Deferred Cost of Sales, Prior to Transition Adjustment	6,415
Deferred Cost of Sales, Transition Adjustment	(2,565)
Deferred Cost of Sales, Write-off of Customer Contracts Where Collection is No Longer Reasonably Assured	$ (1,438)