Segment and Geographic Information - Additional Information (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Segment	Sep. 30, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment			2
Real Estate Services [Member]
Segment Reporting Information [Line Items]
Collection of receivables and associated expenses	$ 0.4	$ 1.5	$ 1.6	$ 4.5
Nasdaq [Member] | Financial Services [Member]
Segment Reporting Information [Line Items]
Other income (loss)	$ 57.4	$ 45.9	$ 58.2	$ 45.3