Description of Trust and Reporting Policies - Additional Information (Detail) (USD $)		1 Months Ended
	Jun. 30, 2014	Aug. 30, 2014 Subsequent Event [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Accrued dividends and interest income	$ 4,700,000
Accrued dividends	4,580,000
Accrued interest income	$ 155,000
Dividends declared per share for accrued dividend		$ 0.30
Accrued dividends record date		Sep. 10, 2014