Fair Value of Financial Instruments (Nonrecurring) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property and equipment, net	$ 447,659	$ 449,199
Capitalized data and database costs, net	329,403	327,921
Investment in affiliates, net	38,989	40,809
Mercury, Inc. [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Call option, fair value				$ 4,600
Myriad Development, Inc. [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liability	3,000
Contingent consideration change in value	300
Insignificant Acquisition
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liability	17,500
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property and equipment, net		0	$ 0
Capitalized data and database costs, net		0
Investment in affiliates, net	0	5,662
Non-financial instruments	0	5,662
Impairment Losses	3,811	26,318
Fair Value, Measurements, Nonrecurring [Member] | Insignificant Acquisition
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liability	4,400
Fair Value, Measurements, Nonrecurring [Member] | Property and equipment, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment Losses		2,005	3,770
Fair Value, Measurements, Nonrecurring [Member] | Equity Method Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment Losses	3,811	23,431
Fair Value, Measurements, Nonrecurring [Member] | Capitalized Data [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment Losses		882
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property and equipment, net		0	0
Capitalized data and database costs, net		0
Investment in affiliates, net	0	0
Non-financial instruments	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property and equipment, net		0	0
Capitalized data and database costs, net		0
Investment in affiliates, net	0	0
Non-financial instruments	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property and equipment, net		0	$ 0
Capitalized data and database costs, net		0
Investment in affiliates, net	0	5,662
Non-financial instruments	$ 0	$ 5,662