Segment Information - Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Total identifiable assets	$ 1,862,716	$ 1,364,696
North America
Segment Reporting, Asset Reconciling Item [Line Items]
Total identifiable assets	1,175,154	956,807
Europe And Africa
Segment Reporting, Asset Reconciling Item [Line Items]
Total identifiable assets	579,879	363,857
Australia And New Zealand
Segment Reporting, Asset Reconciling Item [Line Items]
Total identifiable assets	75,095
Corporate Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Total identifiable assets	$ 32,588	$ 44,032