Significant Accounting Policies (Schedule of Prospective Adoption of New Accounting Pronouncements) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	$ 178,785	$ 141,047	$ 166,186	$ 124,499	$ 146,769	$ 128,876	$ 158,805	$ 131,945	$ 135,462	$ 109,318	$ 155,477	$ 115,618	$ 610,517	$ 566,395	$ 515,875
Costs of services, excluding depreciation and amortization ("D&A")													79,013	66,062	56,026
Gross revenue, net of expenses													531,504	500,333	$ 459,849
ASU 2014-09 [Member] | As Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues													610,517	566,395
Costs of services, excluding depreciation and amortization ("D&A")													(79,013)	(66,062)
Gross revenue, net of expenses													531,504	500,333
ASU 2014-09 [Member] | New Revenue Standard Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from inventory sales													346,774	571,134
Revenues													624,417	555,843
Total revenues													971,191	1,126,977
Cost of inventory sold													(306,498)	(513,348)
Costs of services, excluding depreciation and amortization ("D&A")													(133,189)	(113,296)
Gross revenue, net of expenses													$ 531,504	$ 500,333