Basis of Financial Statement Presentation - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment to retained earnings			$ 0
Selling, general and administrative expenses	$ (38,896,000)	$ (33,913,000)
Other income (expense)	134,000	358,000
Accounting Standards Update 2017-07 | Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Selling, general and administrative expenses	62,000	150,000
Other income (expense)	$ 62,000	$ (150,000)