Earnings Per Share - Summary of Earnings Per Share, Basic and Diluted (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]
Net income	$ 68,120	$ 78,620	$ 73,099	$ 64,662	$ 60,071	$ 59,648	$ 54,401	$ 42,079	$ 284,501	$ 216,199	$ 147,335
Denominator for basic earnings per share	82,388	81,974	81,573	81,222	83,378	84,002	83,294	82,565	81,793	83,328	80,610
Dilutive securities									2,862	2,408	3,044
Denominator for diluted earnings per share	85,277	84,905	84,461	83,960	85,750	86,224	85,737	85,164	84,655	85,736	83,654
Basic earnings per share	$ 0.83	$ 0.96	$ 0.90	$ 0.80	$ 0.72	$ 0.71	$ 0.65	$ 0.51	$ 3.48	$ 2.59	$ 1.83
Diluted earnings per share	$ 0.80	$ 0.93	$ 0.87	$ 0.77	$ 0.70	$ 0.69	$ 0.63	$ 0.49	$ 3.36	$ 2.52	$ 1.76