Summary of Significant Accounting Policies Net income (Loss) Per Common Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average common shares outstanding (basic)	173,325	175,721	186,219
Impact of common stock equivalents	1,093	1,053	962
Weighted average common shares outstanding (diluted)	174,418	176,774	187,181
Stock Options
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	500	1,700	2,800