Employee Benefit Plans - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) plan	Dec. 31, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of pension plans | plan	2
Estimated contributions in the next fiscal year	$ 2.9
Accumulated benefit obligation	134.0	$ 127.0
Underfunded status of plan	$ 18.3	$ 21.6
U.K. Plan
Defined Benefit Plan Disclosure [Line Items]
Maximum increase in pensionable earnings	2.00%
Funded percentage (less than)	100.00%
U.K. Plan | Global return fund
Defined Benefit Plan Disclosure [Line Items]
Target allocation in debt securities	22.00%
U.K. Plan | Real estate
Defined Benefit Plan Disclosure [Line Items]
Target allocation in debt securities	6.40%
U.K. Plan | Liability Driven Investments
Defined Benefit Plan Disclosure [Line Items]
Target allocation in debt securities	20.00%
U.K. Plan | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Target allocation in debt securities	13.00%
U.K. Plan | U.K | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation in debt securities	4.80%
U.K. Plan | Other Than United Kingdom | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation in debt securities	33.00%
Canadian Plan | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Target allocation in debt securities	36.00%
Canadian Plan | Canada | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation in debt securities	20.00%
Canadian Plan | Other Than Canada | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation in debt securities	44.00%