Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenues:
Revenues	$ 128,477		$ 259,961
Retained Earnings (Accumulated Deficit)	483,639		483,639			$ 486,957
Total assets	926,934		926,934			784,856
Total liabilities	571,800		571,800			421,621
Net decrease in commissions and fees	(1,068)		(4,915)
Net increase in recurring revenues	442		868
Net decrease in total revenues	(626)		(4,047)
Revenue related to performance obligations	800
Receivables related to contracts with customers	41,400		41,400			38,200
Impairment losses on receivables			0
Contract assets	0		0
Deferred Revenue	13,861		13,861			8,057
Revenue recognized included in deferred income at beginning of quarter	7,400		14,500
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenues:
Revenues		$ 121,581		$ 242,416
Total assets		956,676		956,676
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	1,400		1,400
Deferred Revenue	5,800		5,800
Commissions and fees and recurring revenue
Revenues:
Revenues	127,000		256,900
Analytics
Revenues:
Revenues	11,026		21,065
Deferred Revenue	$ 12,600		$ 12,600			$ 6,900
Analytics | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenues:
Revenues		$ 11,057		$ 22,200