Stock-Based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock based compensation (Textual) [Abstract]
Incremental expense associated with equity modifications	$ 0.0	$ 0.1	$ 0.1	$ 0.5
Stock options [Member]
Stock based compensation (Textual) [Abstract]
Weighted-average grant-date fair value of stock options granted	$ 0.00	$ 23.15	$ 25.37	$ 17.92
Total intrinsic value of stock options exercised	$ 0.7	$ 4.4	$ 8.7	$ 7.4
Total fair value of shares vested	0.8	1.7	2.9	3.8
Unrecognized compensation cost related to non-vested stock-based compensation awards granted	4.5		$ 4.5
Weighted-average remaining period over which cost is expected to be recognized			2 years 4 months 20 days
Restricted stock awards and units [Member]
Stock based compensation (Textual) [Abstract]
Total fair value of shares vested	9.0	1.5	$ 40.0	18.4
Unrecognized compensation cost related to non-vested stock-based compensation awards granted	69.2		$ 69.2
Weighted-average remaining period over which cost is expected to be recognized			2 years 6 months 13 days
Performance-based restricted stock units [Member]
Stock based compensation (Textual) [Abstract]
Total fair value of shares vested	0.1	$ 0.1	$ 5.2	$ 10.1
Unrecognized compensation cost related to non-vested stock-based compensation awards granted	$ 21.2		$ 21.2
Weighted-average remaining period over which cost is expected to be recognized			1 year 9 months 22 days
Target number of performance-based restricted stock units granted during the period		0
Performance-based restricted stock units [Member] | TSR [Member]
Stock based compensation (Textual) [Abstract]
Target number of performance-based restricted stock units granted during the period			132,000	223,000
Award terms			market conditions based on the Company's total stockholder return ("TSR") relative to that of the Russell 2000 Index over the three-year period ending December 31, 2019, vesting in full in three years with the number of shares ultimately earned ranging from zero to 200% of the target number of shares	market conditions based on the Company's TSR relative to that of the Russell 2000 Index over the three-year period ending December 31, 2018, vesting in full in three years with the number of shares ultimately earned ranging from zero to 200% of the target number of shares
Performance-based restricted stock units [Member] | Net income [Member]
Stock based compensation (Textual) [Abstract]
Target number of performance-based restricted stock units granted during the period			132,000
Award terms			performance conditions based on the compound annual growth rate of net income over the three-year period ending December 31, 2019, vesting in full in three years with the number of shares ultimately earned ranging from zero to 200% of the target number of shares.
Performance-based restricted stock units [Member] | Other Goals [Member]
Stock based compensation (Textual) [Abstract]
Target number of performance-based restricted stock units granted during the period	46,000		46,000
Award terms	performance conditions based on achievement of certain individual and team objectives.		performance conditions based on achievement of certain individual and team objectives.
Employee stock purchase plan [Member]
Stock based compensation (Textual) [Abstract]
Unrecognized compensation cost related to non-vested stock-based compensation awards granted	$ 4.3		$ 4.3
Weighted-average remaining period over which cost is expected to be recognized			1 year 1 month 2 days
Shares issued during period under employee stock purchase plan			103,000	89,000
Weighted-average purchase price of shares issued during period under employee stock purchase plan			$ 40.50	$ 38.35