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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 95,509	$ 78,620	$ 259,167	$ 216,381
Denominator for basic and diluted earnings per share:
Denominator for basic earnings per share	83,611	81,974	83,118	81,592
Dilutive securities	2,523	2,931	2,570	2,854
Denominator for diluted earnings per share	86,134	84,905	85,688	84,446
Basic earnings per share	$ 1.14	$ 0.96	$ 3.12	$ 2.65
Diluted earnings per share	$ 1.11	$ 0.93	$ 3.02	$ 2.56