Stock-Based Compensation - Summary of Restricted Stock Awards Activity (Detail) - Restricted Stock $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Shares
Non-vested restricted stock, beginning balance (in shares) | shares	2,156,372
Granted (in shares) | shares	395,146
Vested (in shares) | shares	(744,244)
Cancelled (in shares) | shares	(42,012)
Non-vested restricted stock, ending balance (in shares) | shares	1,765,262
Weighted- Average Grant Date Fair Value Per Share
Weighted average grant date fair value per share, non-vested restricted stock, beginning balance (in dollars per share) | $ / shares	$ 3.71
Weighted average grant date fair value per share, granted (in dollars per share) | $ / shares	12.94
Weighted average grant date fair value per share, vested (in dollars per share) | $ / shares	3.86
Weighted average grant date fair value per share, forfeited (in dollars per share) | $ / shares	3.78
Weighted average grant date fair value per share, non-vested restricted stock, ending balance (in dollars per share) | $ / shares	$ 5.72
Unrecognized compensation expense | $	$ 6.2
Weighted-average remaining period for recognition of unrecognized compensation costs (in years)	1 year 10 months 24 days