Goodwill and Intangible Assets (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Changes in carrying value of goodwill	$ 0
Goodwill	29,518,000	$ 29,518,000
Gross Carrying Amount	1,380,000	1,380,000
Accumulated Amortization	(383,000)	(268,000)
Net	$ 997,000	$ 1,112,000
Remaining Useful Life (Years)	3 years 1 month	3 years 2 months
Disposal permits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 581,000	$ 581,000
Accumulated Amortization	(205,000)	(180,000)
Net	$ 376,000	$ 401,000
Remaining Useful Life (Years)	5 years 3 months	5 years 6 months
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 799,000	$ 799,000
Accumulated Amortization	(178,000)	(88,000)
Net	$ 621,000	$ 711,000
Remaining Useful Life (Years)	1 year 9 months	2 years
Northeast
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 21,900,000	$ 21,900,000
Rocky Mountain
Finite-Lived Intangible Assets [Line Items]
Goodwill	4,900,000	4,900,000
Southern
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 2,700,000	$ 2,700,000