Summary of Significant Accounting Policies (Earnings Per Share) (Weighted Average Common Shares Outstanding) (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Basic And Diluted Weighted Average Common Shares Outstanding [Line Items]
Basic weighted-average common shares outstanding	210,705	178,594	114,432
Diluted weighted-average common shares outstanding	212,752	180,622	118,439
Employee stock options
Schedule of Basic And Diluted Weighted Average Common Shares Outstanding [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	644	1,699	3,755
Restricted stock awards
Schedule of Basic And Diluted Weighted Average Common Shares Outstanding [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	155	171	170
Performance-based restricted stock awards
Schedule of Basic And Diluted Weighted Average Common Shares Outstanding [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1,248	158	82