Share-Based Compensation (RSUs Vested and Converted) (Details) - RSUs - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs vested during the year	1,337	1,063	954
RSUs converted during the year, net of shares withheld for taxes	865	705	1,238
Shares withheld for taxes	472	358	549