Summary of Significant Accounting Policies - Summary of Basic and Diluted Weighted Average Shares Outstanding (Details) - shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Weighted average basic shares outstanding	129,211	129,177	129,225	131,259	136,876	140,738	142,342	146,322	129,665	141,297	147,326
Effect of dilutive securities:
Unvested performance share awards and share units held by employees (in shares)									189	228	274
Stock options held by employees and directors (in shares)									401	668	902
Diluted weighted average shares outstanding (in shares)	129,728	129,704	129,868	131,942	137,708	141,628	143,224	147,440	130,255	142,193	148,502
Anti-dilutive stock securities (in shares)									863	298	129