Business Acquisition (Narrative) (Details) - USD ($)		3 Months Ended
	Nov. 30, 2016	Apr. 02, 2017	Dec. 31, 2016	Jul. 01, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill				$ 85,463,000	$ 85,463,000
Placemeter
Business Acquisition [Line Items]
Total purchase price	$ 9,600,000
Purchase price, cash paid		$ 800,000	$ 8,800,000
Goodwill	3,742,000
Deferred tax liabilities	308,000
Intangibles	6,000,000
Placemeter | Technology
Business Acquisition [Line Items]
Intangibles	$ 5,500,000
Discount rate used to calculate present value of future cash flows	15.00%
Acquired intangible assets, estimated useful life	4 years
Placemeter | Database
Business Acquisition [Line Items]
Intangibles	$ 200,000
Discount rate used to calculate present value of future cash flows	15.00%
Acquired intangible assets, estimated useful life	4 years
Placemeter | Non-compete Agreements
Business Acquisition [Line Items]
Intangibles	$ 300,000
Discount rate used to calculate present value of future cash flows	20.00%
Acquired intangible assets, estimated useful life	3 years
Placemeter | U.S. Federal
Business Acquisition [Line Items]
Goodwill deductible for income tax purposes	$ 0
Placemeter | U.S. State
Business Acquisition [Line Items]
Goodwill deductible for income tax purposes	$ 0