Stock-based Compensation (Summary of Restricted Stock Activity) (Details) - $ / shares	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, beginning of period, Shares	301,897	384,923
Granted, Shares	141,949	92,409
Vested, Shares	(135,863)	(95,787)
Forfeited, Shares	(18,831)	(20,988)
Outstanding, end of period, Shares	289,152	360,557
Outstanding, beginning of period, Weighted Average Grant Date Fair Value	$ 54.54	$ 45.63
Granted, Weighted Average Grant Date Fair Value	83.47	70.61
Vested, Weighted Average Grant Date Fair Value	42.44	41.56
Forfeited, Weighted Average Grant Date Fair Value	67.15	48.90
Outstanding, end of period, Weighted Average Grant Date Fair Value	$ 73.61	$ 52.93
Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, beginning of period, Shares	196,142	218,338
Granted, Shares	118,736	82,025
Vested, Shares	(144,141)	(77,854)
Forfeited, Shares	(56,500)	(14,451)
Outstanding, end of period, Shares	114,237	208,058
Outstanding, beginning of period, Weighted Average Grant Date Fair Value	$ 47.89	$ 44.24
Granted, Weighted Average Grant Date Fair Value	73.14	48.55
Vested, Weighted Average Grant Date Fair Value	41.11	38.82
Forfeited, Weighted Average Grant Date Fair Value	63.52	44.68
Outstanding, end of period, Weighted Average Grant Date Fair Value	$ 74.97	$ 47.93