Goodwill and Intangible Assets - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	May 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Acquired goodwill		$ 5,158
Impairment of goodwill		0	$ 0	$ 31,558
Amortization of intangible assets		550	$ 36	$ 223
New York
Goodwill [Line Items]
Acquired goodwill		$ 5,158
New York and Boston
Goodwill [Line Items]
Impairment of goodwill	$ 31,558