Description of Business and Summary of Significant Accounting Policies - Narrative (Details)		12 Months Ended
	Aug. 02, 2017 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) investment_type inventory_category	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock issued upon conversion (in shares) | shares	55,422,002
Conversion basis	1
Number of types of investments | investment_type		2
Purchases of investments		$ 2,000,000
Number of inventory categories | inventory_category		3
Real estate rental period		30 days
Intangible assets, useful life		10 years
Goodwill		$ 9,186,000	$ 9,186,000
Goodwill, impaired, accumulated impairment loss		0
Advertising costs		62,536,000	33,457,000	$ 21,902,000
Advertising production costs		2,029,000	$ 1,644,000	$ 1,609,000
Operating lease, right-of-use asset		52,004,000
Operating lease, liability		$ 71,071,000
Vehicles
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lessee, finance lease, term of contract		4 years
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant and equipment, estimated useful lives		P2Y
Operating lease term		1 year
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant and equipment, estimated useful lives		P3Y
Operating lease term		11 years
IPO
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Shares sold in offering (in shares) | shares	10,615,650
Share price (in dollars per share) | $ / shares	$ 15.00
Net proceeds from stock offering	$ 144,380,000
Over-Allotment Option
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Shares sold in offering (in shares) | shares	1,384,650
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset		$ 33,953,000
Operating lease, liability		$ 49,395,000