Fair Value of Financial Instruments - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Acquired Finite-Lived Intangible Assets [Line Items]
Net gain from change in fair value of mortgage loans	$ 4,300,000	$ 1,700,000	$ 775,000
Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets amortized over an estimated useful life	3 years
Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets amortized over an estimated useful life	10 years