Goodwill and Intangible Assets - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill	$ 53,048,000		$ 53,048,000		$ 31,328,000
Impairment of goodwill			0		$ 0
Amortization expense for intangible assets	$ 1,800,000	$ 900,000	$ 2,700,000	$ 1,500,000