Property and Equipment - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Internal-use software development costs not yet subject to amortization	$ 7,800
Depreciation expense	$ 14,188	$ 12,358	$ 12,011