Summary of Significant Accounting Policies - Components of Property, Building and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other Long Term Assets [Line Items]
Property, building and equipment, gross	$ 90,018	$ 78,477
Less accumulated depreciation	43,565	35,226
Property, Plant and Equipment, Net	46,453	43,251
Land [Member]
Other Long Term Assets [Line Items]
Property, building and equipment, gross	2,033	2,033
Building and improvements [Member]
Other Long Term Assets [Line Items]
Property, building and equipment, gross	14,166	11,363
Transportation equipment [Member]
Other Long Term Assets [Line Items]
Property, building and equipment, gross	11,363	11,220
Fixed equipment [Member]
Other Long Term Assets [Line Items]
Property, building and equipment, gross	780	1,090
Office furniture and medical equipment [Member]
Other Long Term Assets [Line Items]
Property, building and equipment, gross	$ 61,676	$ 52,771