Stock Compensation Plans (Summary of Activity for Time-Based and Performance-Based RSUs) (Details)	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Time-Based RSUs Settled in Shares
Shares
Outstanding, at beginning of period (in shares)	1,139,868
Granted (in shares)	606,327
Vested (in shares)	(250,160)
Forfeited (in shares)	(22,182)
Outstanding, at end of period (in shares)	1,473,853
Weighted-Average Grant Date Fair Value
Outstanding, at beginning of period (in dollars per share) | $ / shares	$ 57.78
Granted (in dollars per share) | $ / shares	41.76
Vested (in dollars per share) | $ / shares	54.47
Forfeited (in dollars per share) | $ / shares	52.82
Outstanding, at end of period (in dollars per share) | $ / shares	$ 51.83
Performance-Based RSUs Settled in Shares
Shares
Outstanding, at beginning of period (in shares)	386,483
Granted (in shares)	165,084
Vested (in shares)	(131,597)
Forfeited (in shares)	0
Outstanding, at end of period (in shares)	419,970
Weighted-Average Grant Date Fair Value
Outstanding, at beginning of period (in dollars per share) | $ / shares	$ 60.13
Granted (in dollars per share) | $ / shares	39.79
Vested (in dollars per share) | $ / shares	56.59
Forfeited (in dollars per share) | $ / shares	0
Outstanding, at end of period (in dollars per share) | $ / shares	$ 53.24
Time-Based RSUs Settled in Cash
Shares
Outstanding, at beginning of period (in shares)	11,638
Granted (in shares)	5,639
Vested (in shares)	(600)
Forfeited (in shares)	0
Outstanding, at end of period (in shares)	16,677