CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Property and equipment, Accumulated depreciation	$ 57.8	$ 57.1
Common stock, shares authorized (in shares)	180,000,000	180,000,000
Common stock, issued (in shares)	92,341,484	92,332,565
Common stock, outstanding (in shares)	74,342,826	75,329,557
Treasury stock (in shares)	17,998,658	17,003,008