Preferred Stock - Additional Information (Detail) (USD $)	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Oct. 27, 2014	Jul. 29, 2014	Apr. 30, 2014	Jan. 26, 2015	Apr. 29, 2014
Class of Stock [Line Items]
Amount Of Non Voting Series A Preferred Stock Purchase price	$ 126,000,000
Non-voting Series A Preferred Stock, number of shares issued		1,800	1,800
Non-voting Series A Preferred Stock, maximum aggregate consideration						180,000,000
Redemption of Preferred Stock at original purchase price	$ 10,000
Preferred Stock [Member]
Class of Stock [Line Items]
Estimated fair value of derivatives	3,000,000
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]
Class of Stock [Line Items]
Issuance of non-voting Series A Preferred Stock, shares issued				9,000
Additional shares issued		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
Non-voting Series A Preferred Stock, cumulative, non-participating cash dividend				0.10%
Subsequent Event [Member]
Class of Stock [Line Items]
Non-voting Series A Preferred Stock, number of shares issued					1,800
Subsequent Event [Member] | Non-Voting Series A Preferred Stock [Member]
Class of Stock [Line Items]
Additional shares issued					1,800
Amount Of Non Voting Series A Preferred Stock Purchase price					$ 18,000,000