Business and Basis of Presentation - Schedule of Contract with Customer, Asset and Liability (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Assets:
Fees receivable, gross	$ 1,091,190		$ 1,091,190		$ 1,162,871
Contract assets	31,911		31,911		26,672
Contract liabilities:
Deferred revenues (current liability)	1,687,724		1,687,724		1,630,198
Non-current deferred revenues	17,859		17,859		16,205
Total contract liabilities	1,705,583		1,705,583		$ 1,646,403
Revenue recognized previously attributable to deferred revenues	651,900		969,300
Revenue reserve balance	6,900		$ 6,900
Amortization of deferred sales commissions, amortization period			1 year
Amortization of deferred sales commissions	$ 76,800	$ 54,700	$ 152,700	$ 104,900