Subsequent Events (Narrative) (Detail) - Subsequent event - USD ($)	Feb. 19, 2019	Feb. 17, 2019
Revolving credit facility | DIP Credit Agreement
Subsequent Event [Line Items]
DIP outstanding facility	$ 60,000,000
Eurodollar Loan | Revolving credit facility | DIP Credit Agreement | Maximum
Subsequent Event [Line Items]
Interest rate	7.00%
ABR Borrowings | Revolving credit facility | DIP Credit Agreement | Maximum
Subsequent Event [Line Items]
Interest rate	6.00%
NMC Atlas, L.P. | Asset Purchase Agreement
Subsequent Event [Line Items]
Aggregate purchase price in cash plus Assumed Liabilities		$ 338,000,000