Common Stock - Restricted Stock Units Activity (Details) (Restricted Stock Units (RSUs), USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Restricted Stock Units (RSUs)
Number of RSUs
Nonvested shares outstanding, January 1, 2013 (in shares)	50,000
Granted (in shares)	98,165
Vested (in shares)	(17,862)	[1]
Forfeited (in shares)	(6,527)	[2]
Nonvested shares outstanding, December 31, 2013 (in shares)	123,776		50,000
Wtd. Avg. Grant Date Fair Value
Nonvested shares outstanding, January 1, 2013 (in dollars per share)	$ 66.16
Granted (in dollars per share)	$ 74.30		$ 71.45	$ 61.24
Vested (in dollars per share)	$ 66.02	[1]
Forfeited (in dollars per share)	$ 71.73	[2]
Nonvested shares outstanding, December 31, 2013 (in dollars per share)	$ 72.35		$ 66.16

[1] Represents the entire amount of RSUs that vested during the year ended December 31, 2013. Of the RSUs that vested, 17,862 were paid out in 2013.

[2] Includes reductions due to employee terminations.