Income Taxes - Carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gross unrecognized tax benefits
Unrecognized tax benefits at the beginning of the period	$ 9,198	$ 1,059	$ 41
Gross increase in tax positions for prior year	157	108	0
Gross increase in tax positions for current year	13,899	8,031	1,018
Unrecognized tax benefits at the end of the period	23,254	$ 9,198	$ 1,059
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	13,900
Federal | Research and Development
Operating Loss Carryforwards [Line Items]
Tax credit carryforward amount	5,400
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	26,400
State | Research and Development
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 7,400