Income Taxes - Net Operating Losses and Income Tax Concessions (Details) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Jan. 01, 2018	Jan. 01, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income taxes
Net operating losses			$ 240.3	$ 106.2
Net operating loss carryforward			23.0	38.6
Valuation allowance			24.6	7.1
Period applicable for additional special income tax concession		5 years
Period applicable for additional special income tax concession, renewal term	5 years
Decrease (increase) in foreign income taxes due to special income tax concession in Singapore			$ 1.3	$ 2.7	$ (7.7)
Impact of income tax concession on basic earnings per common share (in dollars per share)			$ 0.02	$ 0.04	$ (0.11)
Impact of income tax concession on diluted earnings per common share (in dollars per share)			$ 0.02	$ 0.04	$ (0.11)
December 31, 2020
Income taxes
Net operating loss carryforward			$ 0.1
December 31, 2021
Income taxes
Net operating loss carryforward			0.2
December 31, 2022
Income taxes
Net operating loss carryforward			1.2
December 31, 2024
Income taxes
Net operating loss carryforward			0.2
December 31, 2025
Income taxes
Net operating loss carryforward			1.0
December 31, 2026
Income taxes
Net operating loss carryforward			0.2
December 31, 2027
Income taxes
Net operating loss carryforward			0.2
December 31, 2028
Income taxes
Net operating loss carryforward			0.3
December 31, 2029
Income taxes
Net operating loss carryforward			0.8
December 31, 2031
Income taxes
Net operating loss carryforward			0.2
December 31, 2032
Income taxes
Net operating loss carryforward			0.5
December 31, 2033
Income taxes
Net operating loss carryforward			0.1
December 31, 2034
Income taxes
Net operating loss carryforward			0.3
December 31, 2035
Income taxes
Net operating loss carryforward			0.5
December 31, 2036
Income taxes
Net operating loss carryforward			2.7
December 31, 2037
Income taxes
Net operating loss carryforward			5.7
Indefinite
Income taxes
Net operating loss carryforward			$ 8.8