Summary of Significant Accounting Policies Net income (Loss) Per Common Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average common shares outstanding (basic)	175,721	186,219	193,334
Impact of common stock equivalents	1,053	962	1,020
Weighted average common shares outstanding (diluted)	176,774	187,181	194,354
Stock Options
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,700	2,800	3,600