Preferred Stock - Additional Information (Detail) - USD ($)							6 Months Ended
	Jul. 24, 2015	Apr. 27, 2015	Jan. 26, 2015	Oct. 27, 2014	Jul. 29, 2014	Apr. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Apr. 29, 2014
Class of Stock [Line Items]
Amount of Non Voting Series A Preferred Stock Purchase price							$ 36,000,000	$ 90,000,000
Non-Voting Series A Preferred Stock [Member]
Class of Stock [Line Items]
Issuance of non-voting Series A Preferred Stock, shares issued						9,000
Additional shares issued		1,800	1,800	1,800	1,800
Non-voting Series A Preferred Stock, shares purchased price						$ 90,000,000
Amount of Non Voting Series A Preferred Stock Purchase price		$ 18,000,000	$ 18,000,000	$ 18,000,000	$ 18,000,000
Non-voting Series A Preferred Stock, number of shares issued		1,800	1,800	1,800	1,800
Non-voting Series A Preferred Stock, maximum aggregate consideration										$ 180,000,000
Non-voting Series A Preferred Stock, cumulative, non-participating cash dividend						0.10%
Redemption of preferred stock at purchase price							$ 10,000
Non-Voting Series A Preferred Stock [Member] | Maximum [Member]
Class of Stock [Line Items]
Non-voting Series A Preferred Stock, number of shares issued										18,000
Non-Voting Series A Preferred Stock [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Additional shares issued	1,800
Amount of Non Voting Series A Preferred Stock Purchase price	$ 18,000,000
Non-voting Series A Preferred Stock, number of shares issued	1,800
Preferred Stock [Member]
Class of Stock [Line Items]
Derivative instruments, assets							$ 3,000,000		$ 3,000,000