Risk - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016
Unusual Risk or Uncertainty [Line Items]
Percentage of calculation on simple inverse correlation	200.00%
Forward Agreements [Member]
Unusual Risk or Uncertainty [Line Items]
Exposure to swap agreements or forward contracts	100.00%
Ultrashort Fund [Member]
Unusual Risk or Uncertainty [Line Items]
Leverage risk benchmark	50% at any point in the day