Accounting for Stock-based Compensation - Summary of Performance Shares Activity (Details) - Performance Shares - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Number of Shares, Non-vested Beginning Balance	169,486	187,022	129,974
Number of Shares, Granted	85,928	45,136	60,929	107,000
Number of Shares, Vested	(107,000)	(30,576)
Number of Shares, Cancelled		(32,096)	(3,881)
Number of Shares, Non-vested Ending Balance	148,414	169,486	187,022	129,974
Number of Shares, expected to vest in the future	89,525
Weighted-Average Grant Date Fair Value
Weighted-Average Grant Date Fair Value, Non-vested Beginning Balance	$ 45.15	$ 39.95	$ 40.57
Weighted-Average Grant Date Fair Value, Granted	62.07	65.05	38.81
Weighted-Average Grant Date Fair Value, Vested	37.21	44.21
Weighted-Average Grant Date Fair Value, Cancelled		43.72	42.83
Weighted-Average Grant Date Fair Value, Non-vested Ending Balance	60.67	$ 45.15	$ 39.95	$ 40.57
Weighted-Average Grant Date Fair Value, expected to vest in the future	$ 73.83
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Non-vested	$ 13,597,691
Aggregate Intrinsic Value, expected to vest in the future	$ 8,202,281