Stock-Based Compensation (Summary of Activity Under Stock Option Plans) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Options Outstanding
Options outstanding at December 31, 2016 (shares)	116,575
Options exercised (shares)	(22,300)
Options forfeited (shares)	0
Options outstanding at March 31, 2017 (shares)	94,275	116,575
Options exercisable at March 31, 2017 (shares)	94,275
Options vested at December 31, 2016 (shares)	94,275
Weighted- Average Exercise Price Per Share
Options outstanding at December 31, 2016 (in USD per share)	$ 37.76
Options exercised (in USD per share)	34.30
Options forfeited (dollars per share)	0.00
Options outstanding at March 31, 2017 (in USD per share)	37.46	$ 37.76
Options exercisable at March 31, 2017 (in USD per share)	37.46
Options vested at December 31, 2016 (in USD per share)	$ 37.46
Weighted-Average Remaining Contractual Life in Years
Weighted-Average Remaining Contractual Life in Year, Options outstanding	3 years 1 month	3 years 2 months
Options exercisable, Weighted-Average Remaining Contractual Life in Years (years)	3 years 1 month
Options vested, Weighted-Average Remaining Contractual Life in Years (years)	3 years 1 month
Aggregate Intrinsic Value
Options outstanding, Aggregate Intrinsic Value at December 31, 2016	$ 4,552,580
Options outstanding, Aggregate Intrinsic Value, at March 31, 2017	4,563,655	$ 4,552,580
Options exercisable, Aggregate Intrinsic Value	4,563,655
Options vested, Aggregate Intrinsic Value	$ 4,563,655