Description of Business and Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Thousands			3 Months Ended								12 Months Ended
		Jan. 01, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax asset			$ 77,908				$ 61,554				$ 77,908	$ 61,554
Deferred tax asset, valuation allowance			59,939				47,127				59,939	47,127
Deferred contract acquisition costs		$ 30,886	43,669								43,669
Revenue			92,263	$ 83,769	$ 77,436	$ 74,538	$ 72,335	$ 65,304	$ 61,120	$ 58,905	328,006	$ 257,664	$ 200,225
Operating lease liability			$ 9,393								$ 9,393
ASU 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax asset															$ 5,300
Deferred tax asset, valuation allowance															5,300
ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect on financial statements	[1]	24,145
Deferred contract acquisition costs		23,100
Revenue		1,000
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use asset gross														$ 8,400
Reversal of deferred rent														$ 600
Accumulated Deficit | ASU 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect on financial statements															$ 200
Accumulated Deficit | ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect on financial statements	[1]	$ 24,145

[1] Effective January 2018, the Company adopted ASU 2014-09 - Revenue from Contracts with Customers: Topic 606. Accordingly, the Company recorded a net reduction to opening accumulated deficit of $24.1 million as of January 1, 2018 due to the cumulative impact of adopting the new standard. See Note 1 for more information.