Reconciliation of Basic and Diluted Shares Amounts (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income	$ 19,698	$ 14,552	$ 15,861	$ 9,815	$ 3,604	$ 1,659	$ 8,095	$ 8,053	$ 59,926	$ 21,411	$ 16,617
Weighted average shares used in computing net income per share - basic									52,554,000	48,343,000	43,767,000
Effect of dilutive shares:
Options and stock units									971,000	864,000	581,000
Convertible senior notes									366,534	1,123,139	1,123,000
Dilutive potential common shares									1,338,000	864,000	1,704,000
Weighted average shares used in computing net income per share - diluted									53,892,000	49,206,000	45,471,000
Earnings per share:
Basic	$ 0.37	$ 0.28	$ 0.30	$ 0.19	$ 0.07	$ 0.03	$ 0.17	$ 0.18	$ 1.14	$ 0.44	$ 0.38
Diluted	$ 0.36	$ 0.27	$ 0.30	$ 0.18	$ 0.07	$ 0.03	$ 0.17	$ 0.17	$ 1.11	$ 0.44	$ 0.37