Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenues:
Revenues	$ 120,769		$ 380,730
Retained Earnings (Accumulated Deficit)	481,550		481,550			$ 486,957
Total assets	891,759		891,759			784,856
Total liabilities	533,696		533,696			421,621
Net increase (decrease) in commissions and fees	2,106		(2,809)
Net (decrease) increase in recurring revenues	(446)		422
Net increase (decrease) in total revenues	1,660		(2,387)
Revenue related to performance obligations	500
Receivables related to contracts with customers	44,000		44,000			38,200
Impairment losses on receivables			0
Contract assets	0		0
Deferred Revenue	11,593		11,593			8,057
Revenue recognized included in deferred income at beginning of quarter	7,400		21,800
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenues:
Revenues		$ 114,531		$ 356,947
Total assets		794,045		794,045
ASU 2014-09
Revenues:
Retained Earnings (Accumulated Deficit)					$ (50)
ASU 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenues:
Receivables related to contracts with customers	1,100		1,100
Deferred Revenue	3,700		3,700
Commissions and fees and recurring revenue
Revenues:
Revenues	119,300		376,200
Analytics
Revenues:
Revenues	10,825		31,890
Deferred Revenue	$ 10,300		$ 10,300			$ 6,900
Analytics | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenues:
Revenues		$ 11,347		$ 33,547