Common Stock - Non-vested Performance-based Units Activity (Details) (Performance Units, USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Performance Units
Number of Performance Units
Nonvested shares outstanding, January 1, 2013 (in shares)	320,485
Granted (in shares)	104,545		224,560	220,305
Vested (in shares)	(136,282)	[1]
Forfeited (in shares)	(33,311)	[2]
Nonvested shares outstanding, December 31, 2013 (in shares)	255,437		320,485
Wtd. Avg. Grant Date Fair Value
Nonvested shares outstanding, January 1, 2013 (in dollars per share)	$ 67.97
Granted (in dollars per share)	$ 75.00		$ 71.73	$ 63.89
Vested (in dollars per share)	$ 63.95	[1]
Forfeited (in dollars per share)	$ 67.59	[2]
Nonvested shares outstanding, December 31, 2013 (in dollars per share)	$ 72.45		$ 67.97

[1] Represents the entire amount of Performance Shares which vested during the year ended December 31, 2013. Of these vested Performance Shares, 510 were paid out in 2013 and the remainder were outstanding as of December 31, 2013.

[2] Includes reductions due to employee terminations and reductions as a result of the Company not meeting certain performance targets.