Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended			72 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Commitments and Contingencies [Line Items]
Rent expense									$ 8,600	$ 7,500	$ 7,700
Purchase commitment, due in next twelve months	$ 56,900								56,900			$ 56,900
Long-term purchase commitments									2,300
Sales	112,844	$ 99,705	$ 98,244	$ 92,834	$ 106,423	$ 90,250	$ 82,682	$ 81,562	$ 403,627	$ 360,917	$ 325,584
Minimum
Commitments and Contingencies [Line Items]
Length of purchase commitments, in days									60 days
Maximum
Commitments and Contingencies [Line Items]
Length of purchase commitments, in days									120 days
Government Contract
Commitments and Contingencies [Line Items]
Sales												53,500
Charges to income from price adjustment clauses	4,800											4,800
Imputed interest related to price adjustment clauses	500
Total estimated liability	$ 5,300								$ 5,300			$ 5,300
Total sales | Government Contract
Commitments and Contingencies [Line Items]
Total sales, percentage									3.50%