Net Profit per Share - Computation of Basic and Diluted Net Profit Per Share Attributable to Common Stock (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator:
Net income	$ 58,691	$ 66,716	$ 74,253
Denominator:
Weighted-average common shares outstanding, basic (shares)	80,529	77,988	75,825
Dilutive effect of potential common stock (shares)	2,511	2,306	2,255
Total shares, diluted (shares)	83,040	80,294	78,080
Net income per share, basic (usd per share)	$ 0.73	$ 0.86	$ 0.98
Net income per share, diluted (usd per share)	$ 0.71	$ 0.83	$ 0.95