Accounting Standards Updates - Effect on Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 39,078
Marketing expense	912	$ 3,450
Commission expenses	9,305	9,748
Income from operations	1,849	(3,692)
Net income	1,793	$ (4,802)
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	39,078
Marketing expense	1,332
Commission expenses	9,333
Income from operations	1,401
Net income	1,345
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	0
Marketing expense	420
Commission expenses	28
Income from operations	(448)
Net income	$ (448)