Stock-based Compensation (Summary of Restricted Stock Activity) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, beginning of period, Shares	269,063	301,897
Granted, Shares	105,410	128,440
Vested, Shares	(69,030)	(128,525)
Forfeited, Shares	(3,005)	(10,886)
Outstanding, end of period, Shares	302,438	290,926
Outstanding, beginning of period, Weighted Average Grant Date Fair Value	$ 73.91	$ 54.54
Granted, Weighted Average Grant Date Fair Value	91.18	82.75
Vested, Weighted Average Grant Date Fair Value	58.72	41.61
Forfeited, Weighted Average Grant Date Fair Value	82.75	63.18
Outstanding, end of period, Weighted Average Grant Date Fair Value	$ 83.31	$ 72.38
Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, beginning of period, Shares	115,057	196,142
Granted, Shares	54,751	42,681
Vested, Shares	(17,042)	(140,165)
Forfeited, Shares	(2,180)
Outstanding, end of period, Shares	150,586	98,658
Outstanding, beginning of period, Weighted Average Grant Date Fair Value	$ 78.82	$ 47.89
Granted, Weighted Average Grant Date Fair Value	78.76	53.31
Vested, Weighted Average Grant Date Fair Value	57.99	40.95
Forfeited, Weighted Average Grant Date Fair Value	95.36
Outstanding, end of period, Weighted Average Grant Date Fair Value	$ 80.92	$ 60.11