Net Income Per Common Share - Calculation of Diluted Net Income Per Common Share (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net income	$ 79,510	$ 77,993	$ 102,218	$ 112,247
Denominator:
Weighted-average common shares, basic	162,390	154,112	159,198	153,258
Dilutive effect of common stock equivalents	5,680	8,334	5,256	8,190
Weighted-average common shares, diluted	168,070	162,446	164,454	161,448