Stockholders' Equity (Schedule of Deferred Stock Units Transactions) (Details) - Deferred Stock Unit - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Number of Shares
Balance at beginning of the period (in shares)	738,288	692,961	613,754
Issued (in shares)	54,982	56,212	32,462
Granted (in shares)	90,184	187,490	140,461
Dividend equivalents (in shares)	20,922	27,532	(4,505)
Forfeited (in shares)	(23,604)	(38,855)
Exercised (in shares)	(353,259)	(187,052)	(89,211)
Balance at end of the period (in shares)	527,513	738,288	692,961
Dividend equivalent (in usd per share)	$ 59.94	$ 50.45
Forfeited (in usd per share)			$ 30.50
Minimum
Number of Shares
Outstanding exercise price (in usd per share)	6.16	6.16	6.16
Issued (in usd per share)	52.20	36.68	33.84
Granted (in usd per share)	52.20	45.98	36.58
Forfeited (in usd per share)	30.50	26.98
Exercised (in usd per share)	20.89	19.98	20.20
Outstanding exercise price (in usd per share)	6.16	6.16	6.16
Maximum
Number of Shares
Outstanding exercise price (in usd per share)	51.20	50.85	33.32
Issued (in usd per share)	60.92	51.46	48.53
Granted (in usd per share)	61.53	46.95	50.85
Forfeited (in usd per share)	60.29	50.89
Exercised (in usd per share)	51.46	50.89	30.65
Outstanding exercise price (in usd per share)	$ 61.53	$ 51.20	$ 50.85