Property and Equipment (Narratives) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Net book value	$ 57,996	$ 56,942
Depreciation	25,200	22,600	$ 16,800
Software Development
Property, Plant and Equipment [Line Items]
Net book value	33,300	31,800
Software Development Work-in-Progress
Property, Plant and Equipment [Line Items]
Net book value	$ 3,200	$ 3,100