Summary of Significant Accounting Policies - Deferred Customer Acquisition Costs (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Short-term
Balance at December 31, 2019	$ 38,435
Deferred customer acquisition costs incurred in the period	5,653
Amounts recognized as expense in the period	(12,446)
Adjustment resulting from sale of SinglePlatform business	0
Impact of foreign exchange rates	(99)
Reclassification between short-term and long-term	6,878
Balance at March 31, 2020	38,421
Long-term
Balance at December 31, 2019	48,780
Prepaid commissions, net of current portion	48,780
Deferred customer acquisition costs incurred in the period	10,156
Amounts recognized as expense in the period	0
Impact of foreign exchange rates	7
Adjustment resulting from sale of SinglePlatform business	(15)
Reclassification between short-term and long-term	(6,878)
Balance at March 31, 2020	$ 52,050