Summary of All Restricted Stock Activity (Detail) - Restricted Stock - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding at December 31, 2014	1,288,769
Granted, Number of shares	667,126	572,052	521,181
Vested, Number of shares	(396,389)
Forfeited, Number of shares	(21,390)
Options Outstanding at December 31, 2015	1,538,116	1,288,769
Options Outstanding, Weighted Average Grant Date Fair Value	$ 11.70
Granted, Weighted Average Grant Date Fair Value	14.84
Vested, Weighted Average Grant Date Fair Value	10.84
Forfeited, Weighted Average Grant Date Fair Value	13.44
Options Outstanding, Weighted Average Grant Date Fair Value	$ 13.25	$ 11.70