Stock-Based Compensation - Summary of PSU Activity (Details) - Performance-Based Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Units
Balance at the beginning of the period (in shares)	30,071	0
Granted (in shares)	28,735	30,071
Balance at the end of the period (in shares)	58,806	30,071
Weighted-Average Grant-Date Fair Value
Balance at the beginning of the period (in dollars per share)	$ 83.84	$ 0.00
Granted (in dollars per share)	96.19	83.84
Balance at the end of the period (in dollars per share)	$ 89.87	$ 83.84