Income Taxes (Details) $ / shares in Units, $ in Millions, ₩ in Billions	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares	Mar. 31, 2018 KRW (₩)	Mar. 31, 2017 USD ($) $ / shares
Income tax provision	$ 7.3		$ 5.0
Effective income tax rate	19.00%	19.00%	13.90%
Effective income tax rate reconciliation, valuation allowance on U.S. deferred tax assets	$ 4.9
Income tax expense due to change in estimate related to uncertain tax position and adjustment for ASU 2016-09			$ 1.2
Special income tax concession period	5 years	5 years
Decrease in foreign income taxes due to special income tax concession	$ (0.1)		$ 0.8
Impact of income tax concession on basic earnings per common share (in dollars per share) | $ / shares	$ 0		$ 0.01
Impact of income tax concession on diluted earnings per common share (in dollars per share) | $ / shares	$ 0		$ 0.01
Tax Authority, South Korea (SRTO)
Income tax assessment notice, amount	$ 10.6	₩ 11.3
Without income tax benefit adjustment and valuation allowance
Effective income tax rate	31.70%	31.70%	10.60%