Share-Based Payments - SOP 2015 (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Additional disclosures
Share-based compensation expense	$ 5,219	$ 9,748	$ 5,154
Stock Option Plan 2015
Options
Outstanding at beginning of year (in shares)	229,060	284,291	304,489
Forfeited (in shares)	(26,686)	(55,231)	(20,198)
Outstanding at end of year (in shares)	202,374	229,060	284,291
Vested and exercisable at end of year (in shares)	198,574	198,491	184,459
Weighted average exercise price in $ per share
Outstanding balance at beginning of year (in dollars per share)	$ 83.27	$ 83.41	$ 83.54
Forfeited (in dollars per share)	87.46	84.01	84.07
Outstanding balance at end of year (in dollars per share)	82.71	83.27	83.41
Vested and exercisable balance at end of year (in dollars per share)	$ 82.51	$ 81.98	$ 80.97
Fair Value Assumptions
Recognition period	2 months 12 days
Stock Option Plan 2015 | $4.06 per share to $11.00 per share
Additional disclosures
Exercise price minimum range	$ 40.60
Exercise price maximum range	$ 110.00
Weighted average remaining contractual life	5 years 4 months 24 days
Stock Option Plan 2015 | Stock Options
Share-Based Payments
Vesting period	4 years
Additional disclosures
Share-based compensation expense	$ 1,100	$ 4,000	$ 3,200
Fair Value Assumptions
Total unrecognized compensation related to unvested options	$ 200
Stock Option Plan 2015 | Stock Options | Maximum
Share-Based Payments
Exercise period	10 years
Stock Option Plan 2015 | Stock Options | Vesting period, year one
Share-Based Payments
Percentage that vests during the period	25.00%
Stock Option Plan 2015 | Stock Options | Vesting period, years 2-4
Share-Based Payments
Percentage that vests during the period	75.00%
Monthly vesting percentage	2.083%