Stockholders' Equity (Schedule of Deferred and Restricted Stock Units Transactions) (Details) - Deferred and Restricted Stock Unit - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Balance at beginning of the period (in shares)	449,055	506,447	527,513
Issued (in shares)	5,354	68,340	10,742
Granted (in shares)	101,650	95,079	173,097
Dividend equivalents (in shares)	8,036	9,799	9,075
Forfeited (in shares)	(9,557)	(3,094)	(10,893)
Vested (in shares)	(290,132)	(227,516)	(203,087)
Balance at end of the period (in shares)	264,406	449,055	506,447
Weighted Average Price
Outstanding exercise price (in usd per share)	$ 72.55	$ 50.00	$ 44.94
Issued (in usd per share)	106.10	108.61	72.01
Granted (in usd per share)	103.20	109.50	54.67
Dividend equivalent (in usd per share)	89.66	104.12	87.01
Forfeited (in usd per share)	76.71	72.96	48.98
Exercised (in usd per share)	74.83	40.39	43.55
Outstanding exercise price (in usd per share)	$ 83.84	$ 72.55	$ 50.00