Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 263,027	$ 257,116	$ 388,788	$ 396,140
Weighted average common shares outstanding - basic (in shares)	111,416	111,036	111,363	110,984
Net effect of dilutive securities:
Contingently issuable performance shares and restricted stock units (in shares)	684	580	624	506
Weighted average common shares outstanding — diluted (in shares)	112,100	111,616	111,987	111,490
Net income attributable to common shareholders - basic (in dollars per share)	$ 2.36	$ 2.32	$ 3.49	$ 3.57
Net income attributable to common shareholders - diluted (in dollars per share)	$ 2.35	$ 2.30	$ 3.47	$ 3.55