Changes in Non-Vested Shares of Restricted Common Stock (Detail) - Restricted Stock - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of shares
Nonvested restricted common stock, beginning balance	259,323	114,505	139,641
Common stock vested	(122,141)	(96,172)	(98,530)
Common stock granted	527,889	255,151	73,394
Common stock forfeited	(67,825)	(14,161)
Nonvested restricted common stock, ending balance	597,246	259,323	114,505
Weighted Average Grant Date Fair Value per share
Nonvested restricted common stock, beginning balance	$ 7.05	$ 4.94	$ 4.94
Common stock vested	7.23	6.92	5.76
Common stock granted	6.64	6.89	9.89
Common stock forfeited	6.88	8.08
Nonvested restricted common stock, ending balance	$ 6.63	$ 7.05	$ 4.94