Earnings per Common Share - Reconciliation of Numerators and Denominators of Basic and Diluted Earnings Per Common Share Computations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basic:
Net income (loss) attributable to common stockholders													$ 5,285	$ (67,138)	$ (37,672)
Weighted average common shares outstanding													55,355,802	53,679,134	52,384,876
Basic earnings (loss) per common share	$ (0.31)	$ (0.21)	$ (0.27)	$ 0.89	$ (0.29)	$ (0.30)	$ (0.31)	$ (0.35)	$ 0.20	$ (0.39)	$ (0.37)	$ (0.16)	$ 0.10	$ (1.25)	$ (0.72)
Effect of dilutive securities:
Net income (loss) attributable to common stockholders	$ (16,210)	$ (11,951)	$ (14,879)	$ 48,325	$ (15,942)	$ (15,977)	$ (16,486)	$ (18,733)	$ 10,171	$ (20,439)	$ (19,211)	$ (8,193)	$ 5,285	$ (67,138)	$ (37,672)
Adjustment to income for dilutive options and warrants													0	0	0
Net income (loss), diluted, Total													$ 5,285	$ (67,138)	$ (37,672)
Weighted average common shares outstanding													55,355,802	53,679,134	52,384,876
Effect of dilutive options and warrants													1,046,677
Diluted weighted average common shares outstanding													56,402,479	53,679,134	52,384,876
Diluted earnings (loss) per common share	$ (0.30)	$ (0.21)	$ (0.27)	$ 0.87	$ (0.29)	$ (0.30)	$ (0.31)	$ (0.35)	$ 0.20	$ (0.39)	$ (0.37)	$ (0.16)	$ 0.09	$ (1.25)	$ (0.72)