Capital Stock (Details) $ / shares in Units, $ in Millions	1 Months Ended
	Nov. 30, 2014 USD ($) $ / shares shares	Dec. 31, 2016 vote shares	Dec. 31, 2015 shares
Capital Stock
Authorized share capital (in shares) | shares		233,333,000	233,333,000
Number of votes per share | vote		1
Shareholder ownership threshold for voting rights (as a percent)		9.50%
Minimum number of votes per share for other shareholders under 9.5% shareholder provision | vote		1
Maximum number of votes per share for certain shareholders under 9.5% shareholder provision | vote		1
Public offering
Capital Stock
Shares issued (in shares) | shares	6,000,000
Share price (in dollars per share) | $ / shares	$ 22.25
Shares sold by selling shareholders (in shares) | shares	7,800,000
Net proceeds from sale of stock | $	$ 126.7