Property and Equipment, net - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 115,047,000	$ 101,001,000
Accumulated amortization	48,106,000	29,611,000
Lease financing obligation	30,900,000	28,900,000
Property and equipment capitalized but not placed in service	4,300,000	5,300,000
Total depreciation and amortization expense	23,345,000	17,646,000	$ 13,213,000
Capitalized Facility Lease
Property, Plant and Equipment [Line Items]
Property and equipment, gross	39,302,000	39,154,000
Interest costs capitalized related to premises	0	2,000,000	0
Accumulated amortization	1,200,000	200,000
Depreciation and amortization expense	1,000,000	200,000
Property and Equipment
Property, Plant and Equipment [Line Items]
Total depreciation and amortization expense	19,300,000	13,500,000	8,900,000
Software Development
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 14,700,000	$ 8,800,000	$ 5,700,000