Business and Basis of Presentation - Schedule of Contract with Customer, Asset and Liability (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Assets:
Fees receivable, gross	$ 1,142,064		$ 1,162,871
Contract assets	27,593		26,672
Contract liabilities:
Deferred revenues (current liability)	1,719,637		1,630,198
Non-current deferred revenues	16,139		16,205
Total contract liabilities	1,735,776		$ 1,646,403
Revenue recognized previously attributable to deferred revenues	605,500
Revenue reserve balance	$ 6,900
Amortization of deferred sales commissions, amortization period	1 year
Amortization of deferred sales commissions	$ 75,900	$ 50,200