Reconciliation of Earnings Per Share (EPS) - Earnings Per Share Reconciliation (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share Reconciliation
Net Income, Basic EPS	$ 53,316	$ 56,692
Basic Shares Outstanding (in shares)	72,629	72,143
Earnings Per Share, Basic (in dollars per share)	$ 0.73	$ 0.79
Effect of dilutive securities
Net Income, Diluted EPS	$ 53,316	$ 56,692
Diluted Shares Outstanding (in shares)	73,045	72,288
Earnings Per Share, Diluted (dollars per share)	$ 0.73	$ 0.78
Stock options
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	296	144
Non-vested restricted stock
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	44	1
Performance share awards
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	0	0