Stock-Based Compensation (Nonvested Performance-based Award Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Incentive Stock Awards [Member]
Non-vested PVS Awards [Roll Forward]
Granted at target level	2,400	1,500	4,200
Forfeited	(800)	(200)	(4,100)
Non-vested PVS Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Granted at target level	$ 59.64	$ 51.53	$ 48.69
Performance-Vesting Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares to be issued upon conversion	362,939
Average remaining term of shares issued at conversion	1 year
Non-vested PVS Awards [Roll Forward]
Outstanding, Beginning	422,726	470,719	578,358
Granted at target level	115,035	147,908	133,823
Adjustments above/(below) target	(19,339)	(132,444)	(53,438)
Vested and converted	(173,364)	(318,337)	(250,205)
Forfeited	(5,674)	(10,008)	(44,695)
Outstanding, Ending	378,062	422,726	470,719
Non-vested PVS Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding, Beginning (in usd per share)	$ 45.60	$ 30.93	$ 23.79
Granted at target level	60.47	55.49	47.21
Adjustments above/(below) target	38.71	22.97	22.86
Vested and converted	59.64	51.53	48.69
Forfeited	49.86	41.84	30.76
Outstanding, Ending (in usd per share)	$ 54.47	$ 45.60	$ 30.93
Performance-Vesting Units [Member]
Non-vested PVS Awards [Roll Forward]
Outstanding, Beginning	29,196	55,509	79,456
Granted at target level	419	1,386	1,584
Adjustments above/(below) target	(2,858)	(19,315)	(6,907)
Vested and converted	(29,032)	(47,014)	(32,438)
Forfeited	(990)	0	0
Outstanding, Ending	2,451	29,196	55,509
Non-vested PVS Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding, Beginning (in usd per share)	$ 32.07	$ 26.15	$ 23.86
Granted at target level	59.64	54.14	47.34
Adjustments above/(below) target	30.80	22.07	22.72
Vested and converted	59.64	51.53	47.34
Forfeited	50.55	0.00	0.00
Outstanding, Ending (in usd per share)	$ 25.28	$ 32.07	$ 26.15
Minimum [Member] | Performance-Vesting Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Actual payout range	0.00%
Minimum [Member] | Performance-Vesting Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Actual payout range	0.00%
Maximum [Member] | Performance-Vesting Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Actual payout range	200.00%
Maximum [Member] | Performance-Vesting Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Actual payout range	200.00%