Reconciliation of Basic and Diluted Shares Amounts (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, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income	$ 12,178	$ 4,669	$ 8,438	$ 3,068	$ 5,029	$ 1,155	$ 3,872	$ 1,625	$ 28,353	$ 11,681	$ 9,345
Denominator:
Basic weighted average common shares outstanding	43,569,000	41,237,000	34,098,000	33,892,000	33,833,000	33,779,000	33,649,000	33,025,000	38,233,527	33,572,883	32,881,940
Effect of dilutive securities:
Stock options and restricted stock awards									441,924	526,015	695,151
Convertible senior notes									474,923
Diluted weighted average common shares outstanding	44,385,000	42,563,000	35,095,000	34,382,000	34,369,000	34,313,000	34,175,000	33,494,000	39,150,374	34,098,898	33,577,091
Basic net income per common share	$ 0.28	$ 0.11	$ 0.25	$ 0.09	$ 0.15	$ 0.03	$ 0.12	$ 0.05	$ 0.74	$ 0.35	$ 0.28
Diluted net income per common share	$ 0.27	$ 0.11	$ 0.24	$ 0.09	$ 0.15	$ 0.03	$ 0.11	$ 0.05	$ 0.72	$ 0.34	$ 0.28