Incentive Award Plan - Schedule of Nonvested Restricted Stock Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of Nonvested Shares of Restricted Common Stock
Number of Nonvested Shares of Restricted Common Stock, Balance	287,827
Restricted stock
Number of Nonvested Shares of Restricted Common Stock
Number of Nonvested Shares of Restricted Common Stock, Balance	333,441	320,017	140,468
Number of Nonvested Shares of Restricted Common Stock, Granted	103,704	152,103	243,233
Number of Nonvested Shares of Restricted Common Stock, Forfeited	(23,968)	(31,925)	(29,664)
Number of Nonvested Shares of Restricted Common Stock, Vested	(125,350)	(106,754)	(34,020)
Number of Nonvested Shares of Restricted Common Stock, Balance	287,827	333,441	320,017
Weighted-Average Grant Date Fair Value per Share
Weighted-Average Grant Date Fair Value per Share, Balance	$ 14.30	$ 14.30	$ 14.00
Weighted-Average Grant Date Fair Value per Share, Granted	18.03	15.34	14.40
Weighted-Average Grant Date Fair Value per Share, Forfeited	15.37	14.54	14.04
Weighted-Average Grant Date Fair Value per Share, Vested	14.63	14.34	14.00
Weighted-Average Grant Date Fair Value per Share, Balance	$ 15.92	$ 14.30	$ 14.30
Fair value of vested shares	$ 2.6	$ 1.6	$ 0.5
Shares tendered for tax withholding requirements	36,374	12,670	6,928