Significant Business Transactions and Events - Acquisition of KRFS (Details) - USD ($) $ in Millions		12 Months Ended
	Feb. 24, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2015
Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed
Goodwill		$ 516.4	$ 799.1	$ 458.3
Kaufman Rossin Fund Services LLC
Consideration
Cash paid	$ 94.7
Goodwill, expected tax deductible amount	61.0
Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed
Cash and cash equivalents	1.0
Accounts receivable	2.9
Other current assets	0.1
Investments	0.5
Properties	6.8
Intangible assets	23.4
Goodwill	61.0
Total assets	95.7
Deferred revenue	0.6
Other current liabilities	0.4
Total liabilities	1.0
Net assets acquired	94.7
Finite-lived Intangible Assets Acquired	23.4
Total revenue of acquiree since acquisition date		20.9
Net pretax income or loss acquiree since acquisition date		$ 1.1
Acquired software | Kaufman Rossin Fund Services LLC
Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed
Properties	$ 6.5
Weighted average useful life	6 years
Client relationships | Kaufman Rossin Fund Services LLC
Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed
Finite-lived Intangible Assets Acquired	$ 22.5
Weighted average useful life	10 years
Other intangible assets | Kaufman Rossin Fund Services LLC
Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed
Finite-lived Intangible Assets Acquired	$ 0.9
Weighted average useful life	3 years