Share-Based Compensation - Compensation Expense and Information on Non-Vested Shares (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
RSUs [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested, Shares, Beginning balance	732
Unvested, Weighted-average grant-date fair value, Beginning balance	$ 33.33
Forfeited, Shares	(46)
Forfeited, Weighted-average grant-date fair value	$ 35.63
Vested, Shares	(226)
Vested, Weighted-average grant-date fair value	$ 32.64
Granted, Shares	207
Granted, Weighted-average grant-date fair value	$ 29.89
Unvested, Shares, Ending balance	667
Unvested, Weighted-average grant-date fair value, Ending balance	$ 32.37
Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested, Shares, Beginning balance	729	[1]
Unvested, Weighted-average grant-date fair value, Beginning balance	$ 40.41
Forfeited, Shares	(343)
Forfeited, Weighted-average grant-date fair value	$ 38.24
Vested, Shares	(31)
Vested, Weighted-average grant-date fair value	$ 35.49
Granted, Shares	203
Granted, Weighted-average grant-date fair value	$ 29.15
Unvested, Shares, Ending balance	558	[1]
Unvested, Weighted-average grant-date fair value, Ending balance	$ 37.92
Deferred Compensation, Share-based Payments [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested, Shares, Ending balance	20
Unvested, Weighted-average grant-date fair value, Ending balance	$ 40.54
Vested, Shares, Ending Balance	116
Vested, Weighted-average grant-date fair value, Ending balance	$ 34.36
Outstanding, Shares, End Balance	136
Outstanding, Weighted-average grant-date fair value, Ending balance	$ 35.27

[1] 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.