Fair Value Measurements - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Carrying Value
Assets:
Commodity swaps, options and basis swaps		$ 30,688	$ 13,483
Marketable securities	[1]	64,784	61,717
(Liabilities):
Commodity swaps, options and basis swaps		(48,825)	(189,500)
Bank credit facility	[2]	(1,086,000)	(882,000)
Deferred compensation plan	[3]	(106,008)	(139,580)
Fair Value
Assets:
Commodity swaps, options and basis swaps		30,688	13,483
Marketable securities	[1]	64,784	61,717
(Liabilities):
Commodity swaps, options and basis swaps		(48,825)	(189,500)
Bank credit facility	[2]	(1,086,000)	(882,000)
Deferred compensation plan	[3]	(106,008)	(139,580)
5.75% Senior Notes Due 2021 | Carrying Value
(Liabilities):
Senior notes	[2]	(475,952)	(475,952)
5.75% Senior Notes Due 2021 | Fair Value
(Liabilities):
Senior notes	[2]	(493,567)	(496,180)
5.00% Senior Notes Due 2022 | Carrying Value
(Liabilities):
Senior notes	[2]	(580,032)	(580,032)
5.00% Senior Notes Due 2022 | Fair Value
(Liabilities):
Senior notes	[2]	(579,342)	(577,132)
5.875% Senior Notes Due 2022 | Carrying Value
(Liabilities):
Senior notes	[2]	(329,244)	(329,244)
5.875% Senior Notes Due 2022 | Fair Value
(Liabilities):
Senior notes	[2]	(339,464)	(343,648)
Other Senior Notes Due 2022 | Carrying Value
(Liabilities):
Senior notes	[2]	(590)	(1,090)
Other Senior Notes Due 2022 | Fair Value
(Liabilities):
Senior notes	[2]	(584)	(1,104)
5.00% Senior Notes Due 2023 | Carrying Value
(Liabilities):
Senior notes	[2]	(741,531)	(741,531)
5.00% Senior Notes Due 2023 | Fair Value
(Liabilities):
Senior notes	[2]	(738,164)	(735,043)
4.875% Senior Notes Due 2025 | Carrying Value
(Liabilities):
Senior notes	[2]	(750,000)	(750,000)
4.875% Senior Notes Due 2025 | Fair Value
(Liabilities):
Senior notes	[2]	(736,028)	(724,688)
5.75% Senior Subordinated Notes Due 2021 | Carrying Value
(Liabilities):
Subordinated debt	[2]	(22,214)	(22,214)
5.75% Senior Subordinated Notes Due 2021 | Fair Value
(Liabilities):
Subordinated debt	[2]	(22,596)	(22,325)
5.00% Senior Subordinated Notes Due 2022 | Carrying Value
(Liabilities):
Subordinated debt	[2]	(19,054)	(19,054)
5.00% Senior Subordinated Notes Due 2022 | Fair Value
(Liabilities):
Subordinated debt	[2]	(18,692)	(18,387)
5.00% Senior Subordinated Notes Due 2023 | Carrying Value
(Liabilities):
Subordinated debt	[2]	(7,712)	(7,712)
5.00% Senior Subordinated Notes Due 2023 | Fair Value
(Liabilities):
Subordinated debt	[2]	$ (7,671)	$ (7,645)

[1] Marketable securities, which are held in our deferred compensation plans, are actively traded on major exchanges.

[2] The book value of our bank debt approximates fair value because of its floating rate structure. The fair value of our senior notes and our senior subordinated notes is based on end of period market quotes which are Level 2 inputs.

[3] The fair value of our deferred compensation plan is updated at the closing price on the balance sheet date which is a Level 1 input.