Revenue Impact of ASC 606 in Current Period Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended								12 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
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 340,378	$ 327,169	$ 360,460	$ 372,033	$ 370,124	$ 343,236	$ 331,514	$ 247,739	$ 1,400,040	$ 1,292,613	$ 379,372
Increase (Decrease) in Revenue									(11,117)
Cost of Revenue									830,012
Increase (Decrease) Cost of Goods Sold									3,405
Gross Profit	$ 134,640	$ 134,587	$ 151,800	$ 149,001	$ 137,490	$ 111,598	$ 88,062	$ 88,945	570,028	$ 426,095	$ 201,398
Increase (Decrease) Gross Profit									7,712
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues									1,388,923
Cost of Revenue									826,607
Gross Profit									$ 562,316