Stock-Based Compensation (Restricted Stock Units Activity) (Details) - Restricted stock units [Member] - $ / shares	12 Months Ended			36 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
RSUs Outstanding, Beginning Balance, Unvested	527,465	604,879	541,245	541,245
RSUs Outstanding, Beginning Balance, Vested but Deferred	0	3,279	9,748	9,748
RSUs Outstanding, Beginning Balance	527,465	608,158	550,993	550,993
RSUs Outstanding, Beginning Balance, Weighted Average Grant Date Value per RSU	$ 89.53	$ 77.52	$ 75.77	$ 75.77
Target performance share awards granted	233,618	243,614	331,470
Granted, Vested but Deferred	0	0	0
Granted	233,618	243,614	331,470
Granted, Weighted Average Grant Date Value per RSU	$ 135.67	$ 108.60	$ 78.33
Dividend equivalents, Unvested		0	0
Dividends equivalents, Vested but Deferred		16	78
Dividends equivalents		16	78
Dividends equivalents, Weighted Average Grant Date Value per RSU		$ 73.28	$ 60.99
Vested, Unvested	(269,917)	(279,774)	(212,005)
Vested, Vested but Deferred	0	0	0
Vested	(269,917)	(279,774)	(212,005)
Vested, Weighted Average Grant Date Value per RSU	$ 95.67	$ 80.68	$ 75.38
Issued, Unvested		0	0
Issued, Vested but Deferred		(3,295)	(6,547)
Issued		(3,295)	(6,547)
Issued, Weighted Average Grant Date Value per RSU		$ 73.28	$ 49.40
Forfeited, Unvested	(31,721)	(41,254)	(55,831)
Forfeited, Vested but Deferred	0	0	0
Forfeited	(31,721)	(41,254)	(55,831)
Forfeited, Weighted Average Grant Date Value per RSU	$ 100.71	$ 86.47	$ 76.49
RSUs Outstanding, Ending Balance, Unvested	459,445	527,465	604,879	459,445
RSUs Outstanding, Ending Balance, Vested but Deferred	0	0	3,279	0
RSUs Outstanding, Ending Balance	459,445	527,465	608,158	459,445
RSUs Outstanding, Ending Balance, Weighted Average Grant Date Value per RSU	$ 108.61	$ 89.53	$ 77.52	$ 108.61