(Effects of Dilutive Common Stock on Weighted-Average Number of Shares) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator:
Net Income	$ 42,354	$ 34,618	$ 57,829	$ 45,963
Weighted Average Shares of Common Stock Outstanding:
Common Shares Issued	41,659	41,427	41,639	41,404
Fully Vested Deferred Stock Units	122	171	120	165
Total Weighted Average Shares of Common Stock Outstanding and Participating Securities - Basic	41,781	41,598	41,759	41,569
Effect of Dilutive Securities:
Options and Stock Issuable Under Share-Based Compensation Plans	364	323	356	329
Total Shares - Diluted	42,145	41,921	42,115	41,898