Capital Stock and Equity Compensation (Summary of Activity Under Stock Option Plans) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2019
Options Outstanding
Options outstanding at beginning of period (shares)	10,950
Options exercised (shares)	(8,250)
Options forfeited (shares)	(300)
Options outstanding, vested and exercisable at end of period (shares)	2,400	10,950
Weighted- Average Exercise Price Per Share
Options outstanding at beginning of period (in dollars per share)	$ 31.99
Options exercised (in dollars per share)	34.55
Options forfeited (in dollars per share)	23.86
Options outstanding, vested and exercisable at end of period (in dollars per share)	$ 24.20	$ 31.99
Share Based Compensation Arrangement By Share Based Payment Award Options Weighted Average Remaining Contractual Term
Weighted-Average Remaining Contractual Life in Year, options outstanding, vested and exercisable	10 months 24 days	2 years
Aggregate Intrinsic Value
Aggregate Intrinsic Value, options outstanding, vested and exercisable (amount), beginning of period	$ 734,469
Aggregate Intrinsic Value, options outstanding, vested and exercisable (amount), end of period	$ 734,469	$ 734,469	$ 323,232