Stock Transactions and Unit Redemptions - Unit Redemption and Share Repurchase Activity (Detail) - USD ($)	1 Months Ended			3 Months Ended			9 Months Ended
	Sep. 30, 2016	Aug. 31, 2016	Jul. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2016	Sep. 30, 2015
Stock Transactions, Parenthetical Disclosures [Abstract]
Redemptions, Number of Units				2,444,069	1,804,365	775,791	5,024,225
Repurchases, Number of Shares	1,195,067	94,003	52,877		797,189	7,187,046	9,326,182	800,000
Total Redemptions and Repurchases, Number of Units and Shares							14,350,407
Redemptions, Average Price Paid per Unit				$ 8.90	$ 8.91	$ 8.59	$ 8.85
Repurchases, Average Price Paid per Share	$ 8.91	$ 8.81	$ 8.78		$ 9.04	$ 8.72	8.77	$ 8.07
Total Redemptions and Repurchases, Average Price Paid per Unit or Share							$ 8.80
Total Redemptions and Repurchases, Approximate Dollar Value of Units and Shares That May Yet Be Redeemed/Purchased Under the Plan	$ 168,103,646			$ 168,103,646			$ 168,103,646