Indebtedness - Subsequent Development - Additional Information (Detail) (USD $)	0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended		0 Months Ended
	Sep. 30, 2014 CommercialBank	Sep. 30, 2014 CommercialBank	Oct. 16, 2014 Subsequent Event CommercialBank	Sep. 30, 2014 Alternate Base Rate	Sep. 30, 2014 Alternate Base Rate Credit Facility	Oct. 16, 2014 Alternate Base Rate Subsequent Event	Sep. 30, 2014 LIBOR Rate	Sep. 30, 2014 LIBOR Rate Credit Facility	Oct. 16, 2014 LIBOR Rate Subsequent Event	Sep. 30, 2014 Minimum	Sep. 30, 2014 Minimum Credit Facility	Oct. 16, 2014 Minimum Subsequent Event	Sep. 30, 2014 Maximum	Sep. 30, 2014 Maximum Credit Facility	Oct. 16, 2014 Maximum Subsequent Event
Debt Instrument [Line Items]
Bank Credit facility, Facility amount	$ 1,750,000,000	$ 1,750,000,000	$ 2,000,000,000
Bank Credit facility, Borrowing base	$ 2,000,000,000	$ 2,000,000,000	$ 3,000,000,000
Percentage holding of commercial banks, Maximum	9.00%	9.00%	6.00%
Number of commercial banks included in current bank group	28	28	29
Notice period for increase in facility amount	20 days		20 days
Maturity date of loan			Oct. 16, 2019
Commitment fee		0.375%	0.30%
Minimum range of base rate				0.50%	0.125%	0.25%	1.50%	1.125%	1.25%
Maximum range of base rate				1.50%	0.75%	1.25%	2.50%	1.75%	2.25%
Interest rate margin				0.75%		0.50%	1.75%		1.50%
Annual rate of commitment fee paid on the undrawn balance										0.375%	0.15%	0.30%	0.50%	0.30%	0.375%