Fair Value Measurements - Assets and Liabilities Measured on Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Assets:
Trading securities	$ 0.9	$ 2.5
Liabilities:
Contingent consideration associated with CDI acquisition		0.3
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Trading securities	0.9	2.5
Liabilities:
Contingent consideration associated with CDI acquisition		0.0
Significant Other Observable Inputs (Level 2)
Assets:
Trading securities
Liabilities:
Contingent consideration associated with CDI acquisition		0.0
Unobservable Inputs (Level 3)
Assets:
Trading securities	$ 0.0	0.0
Liabilities:
Contingent consideration associated with CDI acquisition		$ 0.3