Calculation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																								12 Months Ended
	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2015	[1]	Jun. 30, 2015	[1]	Mar. 31, 2015	[1]	Dec. 31, 2014	[1]	Sep. 30, 2014	[1]	Jun. 30, 2014	[1]	Mar. 31, 2014	[1]	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Basic net income per share:
Net income applicable to common stockholders																									$ 119,433	$ 104,289	$ 60,930
Undistributed earnings allocated to participating securities																									0	0	(481)
Net income applicable to common stockholders excluding amounts applicable to participating securities																									$ 119,433	$ 104,289	$ 60,449
Weighted average common shares outstanding																									63,729	67,201	68,895
Basic net income per share	$ 0.37		$ 0.52		$ 0.55		$ 0.42		$ 0.50		$ 0.48		$ 0.42		$ 0.15		$ 0.28		$ 0.26		$ 0.23		$ 0.11		$ 1.87	$ 1.55	$ 0.88
Diluted net income per share:
Net income applicable to common stockholders																									$ 119,433	$ 104,289	$ 60,930
Undistributed earnings allocated to participating securities																									0	0	(481)
Net income applicable to common stockholders excluding amounts applicable to participating securities																									$ 119,433	$ 104,289	$ 60,449
Weighted average common shares outstanding																									63,729	67,201	68,895
Dilutive shares from assumed conversion of convertible senior notes																									794	1,128	1,354
Dilutive stock options and restricted stock																									1,239	1,039	814
Diluted weighted average common shares outstanding																									65,762	69,368	71,063
Diluted net income per share	$ 0.36		$ 0.51		$ 0.53		$ 0.42		$ 0.50		$ 0.47		$ 0.41		$ 0.15		$ 0.27		$ 0.25		$ 0.23		$ 0.10		$ 1.82	$ 1.50	$ 0.85

[1] Basic and diluted net income per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly net income per share may differ from annual net income per share due to rounding.