Property and Equipment, net - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 135,991,000	$ 115,047,000
Accumulated amortization	65,281,000	48,106,000
Lease financing obligation	31,400,000	30,900,000
Property and equipment capitalized but not placed in service	7,800,000	4,300,000
Total depreciation and amortization expense	22,472,000	23,345,000	$ 17,646,000
Capitalized Facility Lease
Property, Plant and Equipment [Line Items]
Property and equipment, gross	39,302,000	39,302,000
Interest Costs Capitalized	0	0
Accumulated amortization	2,200,000	1,200,000
Depreciation and amortization expense	1,000,000	1,000,000	200,000
Property and Equipment
Property, Plant and Equipment [Line Items]
Total depreciation and amortization expense	18,600,000	19,300,000	13,500,000
Software Development
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 13,500,000	$ 14,700,000	$ 8,800,000