Common Stock and Earnings (Loss) Per Share - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended			0 Months Ended	1 Months Ended
	Oct. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Nov. 01, 2012	Nov. 30, 2012
Common Stock And Eps [Line Items]
Stock Issued During Period, Shares, New Issues	6,900,000			6,900,000
Proceeds from Issuance of Common Stock	$ 276,100,000	$ 0	$ 0	$ 276,013,000
Stock Issued During Period, Shares, Acquisitions				891,265
Securities Excluded From Calculation of Basic and Diluted Earnings Per Share (in number of shares)		7,500,000	5,900,000	6,900,000
Amount of Restricted Net Assets for Consolidated and Unconsolidated Subsidiaries		798,800,000
Maximum [Member]
Common Stock And Eps [Line Items]
Average Stock Price		$ 58.80
Reverse Mortgage Solutions Inc [Member]
Common Stock And Eps [Line Items]
Payments to Acquire Businesses, Gross					$ 95,000,000
Stock Issued During Period, Shares, Acquisitions						891,265