Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Long-Lived Assets
Cost	$ 54,662	$ 51,500
Accumulated Depreciation/ Amortization	$ (46,543)	(42,479)
Furniture and fixtures
Long-Lived Assets
Estimated useful lives (in years)	5 years
Cost	$ 2,042	1,904
Accumulated Depreciation/ Amortization	$ (1,298)	(1,005)
Equipment, computer hardware and purchased software | Minimum
Long-Lived Assets
Estimated useful lives (in years)	2 years
Equipment, computer hardware and purchased software | Maximum
Long-Lived Assets
Estimated useful lives (in years)	3 years
Office equipment
Long-Lived Assets
Cost	$ 625	600
Accumulated Depreciation/ Amortization	(513)	(345)
Computer hardware
Long-Lived Assets
Cost	5,700	4,526
Accumulated Depreciation/ Amortization	(4,260)	(3,254)
Purchased software
Long-Lived Assets
Cost	35,148	34,155
Accumulated Depreciation/ Amortization	$ (33,304)	(31,825)
Costs of internal-use software
Long-Lived Assets
Estimated useful lives (in years)	3 years
Cost	$ 7,140	6,479
Accumulated Depreciation/ Amortization	(6,075)	(5,298)
Leasehold improvements
Long-Lived Assets
Cost	4,007	3,836
Accumulated Depreciation/ Amortization	$ (1,093)	$ (752)