Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) reporting_unit segment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Income Tax Contingency [Line Items]
Number of operating segments | segment			2
Number of reporting units | reporting_unit			2
Impairment of goodwill			$ 0
Impairment of Intangible Assets, Finite-lived			$ 0
Weighted average useful life (in years)			3 years 8 months
Additional amortization for acquired intangible assets			$ 9,103,000	$ 8,898,000	$ 7,909,000
Net carrying amount		$ 30,174,000	30,174,000	38,315,000
Amounts due from financial intermediaries classified as cash and cash equivalents		1,800,000	1,800,000	800,000
Allowance for doubtful accounts		214,000	214,000	61,000
Advertising expense			$ 163,200,000	121,100,000	$ 86,200,000
Minimum
Income Tax Contingency [Line Items]
Percentage of tax benefit likely to be realized upon settlement			50.00%
Technology
Income Tax Contingency [Line Items]
Useful life			7 years
Net carrying amount		16,738,000	$ 16,738,000	$ 22,621,000
Lemon Inc.
Income Tax Contingency [Line Items]
Weighted average useful life (in years)	6 years
Lemon Inc. | Technology
Income Tax Contingency [Line Items]
Useful life	7 years		7 years
Net carrying amount		$ 1,600,000	$ 1,600,000
Intangible Assets, Amortization Period | Lemon Inc. | Technology
Income Tax Contingency [Line Items]
Useful life		2 years 6 months	2 years 6 months
Weighted average useful life (in years)			2 years 3 months
Additional amortization for acquired intangible assets			$ 700,000