Income Taxes - Summary of Income Tax Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning of period	$ 14,811	$ 13,939
Unrecognized tax benefits, increases resulting from prior period tax positions	91	8
Unrecognized tax benefits, increases resulting from current period tax positions	2,855	2,840
Unrecognized tax benefits, reductions resulting from lapse of applicable statute of limitations	(3,372)	(1,976)
Unrecognized tax benefits, end of period	$ 14,385	$ 14,811