Segment Reporting - Information about Operations in Different Segments (Parenthetical) (Detail) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended		9 Months Ended
		Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Loss (gain) on disposal of assets		$ (100)		$ (4,818)			$ 1,443	$ (46,362)
Capital expenditures	[1]	18,133		61,569			66,118	216,526
Accrued Capital Expenditures of 2014 [Member]
Segment Reporting Information [Line Items]
Capital expenditures		1,200					10,200
Accrued Capital Expenditures of 2013 [Member]
Segment Reporting Information [Line Items]
Capital expenditures				9,500				18,600
ASA [Member]
Segment Reporting Information [Line Items]
Non-cash impairment charges			$ 4,000		$ 6,600	$ 37,800
Loss (gain) on disposal of assets					$ 3,000
Capital expenditures	[1]	$ 11,648		$ 5,316			$ 41,141	$ 83,613

[1] Total capital expenditures include expenditures for which cash payments were made during the period. Capital expenditures for the three and nine months ended September 30, 2015 included $1.2 million and $10.2 million, respectively, of cash payments for accrued capital expenditures outstanding as of December 31, 2014. Capital expenditures for the three months ended September 30, 2014 exclude $9.5 million in accrued liabilities related to capital expenditures and for the nine months ended September 30, 2014 include $18.6 million of cash payments for accrued capital expenditures outstanding as of December 31, 2013.