Redemption Price Expressed as Percentage of Principal Amount Senior Notes Sold in 2011 (Detail)	0 Months Ended
	Dec. 31, 2014
Senior Notes Due February 2019 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	103.25%
Senior Notes Due February 2019 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	101.625%
Senior Notes Due February 2019 [Member] | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes Due February 2019 [Member] | Debt Instrument Redemption Period Six [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes Due February 2021 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	103.375%
Senior Notes Due February 2021 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	102.25%
Senior Notes Due February 2021 [Member] | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	101.125%
Senior Notes Due February 2021 [Member] | Debt Instrument Redemption Period Six [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes Due February 2021 [Member] | Debt Instrument Redemption Period Seven [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%