Capital Stock and Share-Based Compensation - Fair Value of TSR Performance-Based Restricted Stock Units Estimated Using Monte-Carol Valuation Model (Details) - TSR Performance-based Restricted Stock Units	12 Months Ended
	Dec. 31, 2017 $ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant-date stock price	$ 24.30
Expected volatility	28.60%
Risk-free interest rate	1.44%
Expected annual dividend yield	0.00%
Weighted average fair value	$ 33.31