Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Numerator (basic and diluted):
Net income	$ 177,127		$ 146,120		$ 331,456		$ 293,612
Denominator:
Denominator for basic earnings per share - weighted-average shares	110,278		124,870		110,914		125,920
Effect of stock options	1,801	[1]	2,318	[1]	1,822	[1]	2,341	[1]
Denominator for diluted earnings per share - weighted-average shares	112,079		127,188		112,736		128,261
Earnings per share - basic	$ 1.61		$ 1.17		$ 2.99		$ 2.33
Earnings per share - assuming dilution	$ 1.58		$ 1.15		$ 2.94		$ 2.29

[1] See Note 8 for further discussion on the terms of the Company's share-based compensation plans.