Earnings Per Share - Reconciliation of the average shares outstanding used to compute basic and diluted earnings per share (Details) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Basic weighted average common shares outstanding (in shares)	136,036,192	134,934,892	132,894,179
Effect of dilutive securities - stock awards (in shares)	1,397,623	2,416,417	2,436,014
Diluted weighted average common shares outstanding (in shares)	137,433,815	137,351,309	135,330,193
Common shares issuable upon the exercise of stock options
Anti-dilutive shares excluded from the calculation of diluted earnings per share
Number of anti-dilutive shares excluded from the calculation of diluted earnings per share (in shares)	2,800,000	1,200,000	2,300,000