Revenue Recognition - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Retained earnings	$ 29,617,000	$ 29,549,000
Minimum
Disaggregation of Revenue [Line Items]
Performance obligations, period	12 months
Payment period	30 days
Maximum
Disaggregation of Revenue [Line Items]
Performance obligations, period	60 months
Payment period	90 days
Impact after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Retained earnings	$ 0