Share-Based Compensation - Compensation Expense and Information on Non-Vested Shares (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 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	(107)
Forfeited, Weighted-average grant-date fair value	$ 33.72
Vested, Shares	(252)
Vested, Weighted-average grant-date fair value	$ 32.74
Granted, Shares	238
Granted, Weighted-average grant-date fair value	$ 30.10
Unvested, Shares, Ending balance	611
Unvested, Weighted-average grant-date fair value, Ending balance	$ 32.27
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	(328)
Forfeited, Weighted-average grant-date fair value	$ 38.00
Vested, Shares	(31)
Vested, Weighted-average grant-date fair value	$ 35.49
Granted, Shares	277
Granted, Weighted-average grant-date fair value	$ 29.15
Unvested, Shares, Ending balance	647	[1]
Unvested, Weighted-average grant-date fair value, Ending balance	$ 37.04
Deferred Compensation, Share-based Payments [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested, Shares, Beginning balance	20
Unvested, Weighted-average grant-date fair value, Beginning balance	$ 40.54
Forfeited, Shares	(3)
Forfeited, Weighted-average grant-date fair value	$ 40.54
Vested, Shares	(17)
Vested, Weighted-average grant-date fair value	$ 40.54
Granted, Shares	31
Granted, Weighted-average grant-date fair value	$ 29.73
Unvested, Shares, Ending balance	31
Unvested, Weighted-average grant-date fair value, Ending balance	$ 29.73
Vested, Shares, Ending Balance	103
Vested, Weighted-average grant-date fair value, Ending balance	$ 35.55
Outstanding, Shares, End Balance	134
Outstanding, Weighted-average grant-date fair value, Ending balance	$ 34.20

[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.