Stock-Based Compensation - Summary of Employee and Director Share Grant Activity (Details) - Restricted Stock - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Stock Grants
Balance at the beginning of the period (in shares)	212,608	223,114	266,475
Granted (in shares)	95,671	109,081	85,066
Released (in shares)	(94,164)	(110,724)	(116,656)
Cancelled (in shares)	(5,083)	(8,863)	(11,771)
Balance at the end of the period (in shares)	209,032	212,608	223,114
Weighted-Average Grant-Date Fair Value
Balance at the beginning of the period (in dollars per share)	$ 91.62	$ 80.02	$ 74.76
Granted (in dollars per share)	98.81	101.52	86.14
Released (in dollars per share)	89.43	79.58	72.38
Cancelled (in dollars per share)	93.16	90.11	80.96
Balance at the end of the period (in dollars per share)	$ 95.86	$ 91.62	$ 80.02