Revenue from Contracts with Customers - Unbilled contracts (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Deferred Revenue Arrangement [Line Items]
Contracts expected to be billed remainder of year	$ 8,551
Unbilled Receivables, Expected To Be Billed In 2019	15,792
Unbilled Receivables, Expected To Be Billed In 2020	8,367
Unbilled Receivables, Expected To Be Billed In 2021	2,541
Unbilled Receivables, Expected To Be Billed In 2022	1,795
Unbilled Receivables, Expected To Be Billed Thereafter	1,217
Unbilled Receivables, Not Billable	38,263
ASC 606
Deferred Revenue Arrangement [Line Items]
Contracts expected to be billed remainder of year	8,290
Unbilled Receivables, Expected To Be Billed In 2019	14,724
Unbilled Receivables, Expected To Be Billed In 2020	7,980
Unbilled Receivables, Expected To Be Billed In 2021	2,498
Unbilled Receivables, Expected To Be Billed In 2022	1,775
Unbilled Receivables, Expected To Be Billed Thereafter	1,213
Unbilled Receivables, Not Billable	36,480
Operating Lease Revenues
Deferred Revenue Arrangement [Line Items]
Contracts expected to be billed remainder of year	261
Unbilled Receivables, Expected To Be Billed In 2019	1,068
Unbilled Receivables, Expected To Be Billed In 2020	387
Unbilled Receivables, Expected To Be Billed In 2021	43
Unbilled Receivables, Expected To Be Billed In 2022	20
Unbilled Receivables, Expected To Be Billed Thereafter	4
Unbilled Receivables, Not Billable	$ 1,783