Share-Based Compensation - Compensation Expense and Information on Non-Vested Shares (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested, Shares, Beginning balance	499
Unvested, Weighted-average grant-date fair value, Beginning balance	$ 32.28
Forfeited, Shares	(40)
Forfeited, Weighted-average grant-date fair value	$ 32.99
Vested, Shares	(131)
Vested, Weighted-average grant-date fair value	$ 32.77
Granted, Shares	299	[1]
Granted, Weighted-average grant-date fair value	$ 34.98	[1]
Unvested, Shares, Ending balance	627
Unvested, Weighted-average grant-date fair value, Ending balance	$ 33.42
Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested, Shares, Beginning balance	542	[2]
Unvested, Weighted-average grant-date fair value, Beginning balance	$ 37.10	[2]
Forfeited, Shares	(171)
Forfeited, Weighted-average grant-date fair value	$ 39.67
Granted, Shares	746	[3]
Granted, Weighted-average grant-date fair value	$ 38.09	[3]
Unvested, Shares, Ending balance	1,117	[2]
Unvested, Weighted-average grant-date fair value, Ending balance	$ 37.38	[2]
Deferred Compensation, Share-based Payments [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vested, Shares, Ending Balance	143
One year vest [Member] | Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Shares	35
Granted, Weighted-average grant-date fair value	$ 39.35
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	1 year
Three year graded vest [Member] | Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Shares	455
Granted, Weighted-average grant-date fair value	$ 35.35
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years

[1] The RSUs granted during the six months ended June 30, 2014 include 35 thousand one-year RSUs to non-employee directors under the 1991 Plan. These RSUs have a weighted-average grant-date fair value of $39.35.

[2] Non-vested performance shares are based on a maximum potential payout. Actual shares granted at the end of the performance period may be less than the maximum potential payout level depending on achievement of performance share objectives. Performance shares are based on certain annual management objectives, as determined by the Board of Directors.

[3] The maximum performance shares granted during the six months ended June 30, 2014 include 455 thousand which vest proportionately over a three-year period and have a weighted-average grant-date fair value of $35.35.