Segment Reporting - Information about Operations in Different Segments (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
(Gain) loss on disposal of assets	$ 1,910		$ (35,105)	$ 1,543	$ (41,544)
Capital expenditures	24,013		117,064	47,985	154,957
Accrued Capital Expenditures of 2014 [Member]
Segment Reporting Information [Line Items]
Capital expenditures	7,700			11,000
Accrued Capital Expenditures of 2013 [Member]
Segment Reporting Information [Line Items]
Capital expenditures			19,900		28,200
ASA [Member]
Segment Reporting Information [Line Items]
Non-cash impairment charges		$ 4,200		6,600	37,800
(Gain) loss on disposal of assets				3,300
Capital expenditures	$ 18,669		$ 74,229	$ 29,493	$ 78,297