Summary of Significant Accounting Policies - Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income	$ 12,955	$ 6,803	$ 2,419
Basic:
Weighted average shares of common stock and vested, undelivered restricted stock units outstanding	27,738,178	27,550,044	29,953,798
Diluted:
Weighted average shares of common stock and vested, undelivered restricted stock units outstanding	27,678,959	27,550,044	29,953,798
Effect of potentially dilutive shares	973,855	721,340	819,734
Total weighted average shares of common stock and vested, undelivered restricted stock units outstanding and potentially dilutive shares	28,652,814	28,271,384	30,773,532
Basic:
Net income applicable to common stockholders	$ 12,955	$ 6,803	$ 2,419
Weighted average shares of stock outstanding	27,738,178	27,550,044	29,953,798
Net income per common share	$ 0.47	$ 0.25	$ 0.08
Diluted:
Net income applicable to common stockholders	$ 12,955	$ 6,803	$ 2,419
Weighted average shares of stock outstanding	28,652,814	28,271,384	30,773,532
Net income per common share	$ 0.45	$ 0.24	$ 0.08