Income Taxes - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 56,854	$ 56,341
Unrecognized tax benefits	2,141	$ 1,101	$ 343	$ 161
Uncertain tax positions that would impact the effective tax rate	65
Domestic Tax Authority | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, Sec. 382 limitation	173,400
Gross operating loss carryforwards	4,200
Operating loss carryforwards	169,200
State and Local Jurisdiction | Arizona Department of Revenue
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 142,800