Summary of Significant Accounting Policies - Summary of Adjustments to Quarterly Data Resulting from Adoption of New Standard in Statements of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncement Early Adoption [Line Items]
Income tax benefit	$ (349,080)	$ (71,992)	$ 57,651	$ 112,395	$ (95,581)	$ (13,705)	$ (129,488)	$ (41,976)	$ (251,026)	$ (280,750)	$ (338,677)
Net loss	$ 221,185	$ (127,700)	$ 69,550	$ 170,111	$ (160,709)	$ (41,971)	$ (224,936)	$ (93,772)	$ 333,146	$ (521,388)	$ (713,685)
Basic earnings per share	$ 0.89	$ (0.52)	$ 0.28	$ 0.69	$ (0.66)	$ (0.23)	$ (1.35)	$ (0.56)	$ 1.34	$ (2.75)	$ (4.29)
Diluted earnings per share	$ 0.89	$ (0.52)	$ 0.28	$ 0.69	$ (0.66)	$ (0.23)	$ (1.35)	$ (0.56)	$ 1.34	$ (2.75)	$ (4.29)
Accounting Standards Update 2016-09
New Accounting Pronouncement Early Adoption [Line Items]
Income tax benefit								$ (41,976)
Net loss								$ (93,772)
Basic earnings per share								$ (0.56)
Diluted earnings per share								$ (0.56)
Accounting Standards Update 2016-09 | As Reported
New Accounting Pronouncement Early Adoption [Line Items]
Income tax benefit								$ (44,038)
Net loss								$ (91,710)
Basic earnings per share								$ (0.55)
Diluted earnings per share								$ (0.55)