Share-Based Compensation and Equity - Restricted Stock Unit Activity (Details) - Restricted Stock Units [Member] - $ / shares shares in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Restricted Stock Units
Unvested, Shares, Beginning balance		1,200
Forfeited, Shares		(100)
Vested, Shares		(500)
Granted, Shares	[1]	700
Unvested, Shares, Ending balance		1,300		1,200
Unvested, Weighted-average grant-date fair value, Beginning balance		$ 29.50
Forfeited, Weighted-average grant-date fair value		28.72
Vested, Weighted-average grant-date fair value		30.37
Granted, Weighted-average grant-date fair value		26.81	[1]	$ 26.77	$ 32.74
Unvested, Weighted-average grant-date fair value, Ending balance		$ 27.76		$ 29.50
One year vest [Member]
Restricted Stock Units
Granted, Shares		57
Minimum | One year vest [Member]
Restricted Stock Units
Granted, Weighted-average grant-date fair value		$ 28.80

[1] (1) The RSUs granted during the year ended December 31, 2017 include 57 thousand one-year RSUs to non-employee directors under the 1991 Plan. These RSUs have a weighted-average grant-date fair value of $28.80