Equity - Restricted Stock and performance-based stock units (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2015
Restricted stock
Restricted stock and performance based stock units activity
Outstanding at the beginning of the period (in shares)	180,440	163,569	156,297
Granted (in shares)	110,348	101,348	86,772
Vested (in shares)	(93,366)	(84,477)	(79,500)
Outstanding at the end of the period (in shares)	197,422	180,440	163,569
Restricted stock and performance-based stock units
Restricted stock and performance based stock units activity
Granted (in shares)	182,240	167,375	147,608
Outstanding at the end of the period (in shares)	396,177
Compensation expense
Remaining compensation expense	$ 8,605,000
Restricted stock and performance-based stock units | 2022
Restricted stock and performance based stock units activity
Outstanding at the end of the period (in shares)	164,232
Compensation expense
Remaining compensation expense	$ 5,447,000
Restricted stock and performance-based stock units | 2023
Restricted stock and performance based stock units activity
Outstanding at the end of the period (in shares)	128,282
Compensation expense
Remaining compensation expense	$ 2,855,000
Restricted stock and performance-based stock units | 2024
Restricted stock and performance based stock units activity
Outstanding at the end of the period (in shares)	103,663
Compensation expense
Remaining compensation expense	$ 303,000
Restricted stock and performance-based stock units | Grant Date Price 42.27 | Three year vesting
Restricted stock and performance based stock units activity
Granted (in shares)	95,293
Granted (in dollars per share)	$ 42.27
Restricted stock and performance-based stock units | Grant Date Price 42.27 | TSR Targets
Restricted stock and performance based stock units activity
Granted (in shares)	71,892
Granted (in dollars per share)	$ 42.27
Restricted stock and performance-based stock units | Grant Date Price $39.40 | Vesting Date, May 27, 2021
Restricted stock and performance based stock units activity
Granted (in shares)	12,055
Restricted stock and performance-based stock units | Grant Date Price $48.95 | Three year vesting
Restricted stock and performance based stock units activity
Granted (in shares)		76,464
Granted (in dollars per share)		$ 48.95
Vesting period	3 years
Restricted stock and performance-based stock units | Grant Date Price $49.98 | TSR Targets
Restricted stock and performance based stock units activity
Granted (in shares)		66,027
Granted (in dollars per share)		$ 49.98
Restricted stock and performance-based stock units | Grant Date Price $38.45 | Three year vesting
Restricted stock and performance based stock units activity
Granted (in shares)		15,000
Granted (in dollars per share)		$ 38.45
Vesting period		3 years
Restricted stock and performance-based stock units | Grant Date Price $38.45 | Vesting Date, May 29, 2020
Restricted stock and performance based stock units activity
Granted (in shares)		9,884
Granted (in dollars per share)		$ 38.45
Restricted stock and performance-based stock units | Grant Date Price $43.14 | Three year vesting
Restricted stock and performance based stock units activity
Granted (in shares)	3,000
Granted (in dollars per share)	$ 43.14
Restricted stock and performance-based stock units | Grant Date Price $46.54 | Three year vesting
Restricted stock and performance based stock units activity
Granted (in shares)			78,276
Granted (in dollars per share)			$ 46.54
Vesting period		3 years
Restricted stock and performance-based stock units | Grant Date Price $46.54 | TSR Targets
Restricted stock and performance based stock units activity
Granted (in shares)			60,836
Granted (in dollars per share)			$ 46.54
Restricted stock and performance-based stock units | Grant Date Price $38.18 | Three year vesting
Restricted stock and performance based stock units activity
Vesting period			3 years
Restricted stock and performance-based stock units | Grant Date Price $38.18 | TSR Targets
Restricted stock and performance based stock units activity
Vesting period			4 years
Restricted stock and performance-based stock units | Grant Date Price $38.18 | Accelerated TSR Targets
Restricted stock and performance based stock units activity
Vesting period			3 years
Restricted stock and performance-based stock units | Grant Date Price $44.73 | Vesting Date, May 27, 2021
Restricted stock and performance based stock units activity
Granted (in dollars per share)	$ 39.40
Restricted stock and performance-based stock units | Grant Date Price $44.73 | Vesting Date, May 30, 2019
Restricted stock and performance based stock units activity
Granted (in shares)			8,496
Granted (in dollars per share)			$ 44.73
Performance-based stock units
Restricted stock and performance based stock units activity
Granted (in shares)	71,892	66,027	60,836
Vested (in shares)	(108,720)	(81,574)	(48,225)
Outstanding at the end of the period (in shares)	0
Compensation expense
Compensation expense related to share-based award	$ 7,760,000	$ 7,012,000	$ 6,566,000
Performance-based stock units | 2022
Restricted stock and performance based stock units activity
Outstanding at the end of the period (in shares)	60,836
Performance-based stock units | 2023
Restricted stock and performance based stock units activity
Outstanding at the end of the period (in shares)	66,027
Performance-based stock units | 2024
Restricted stock and performance based stock units activity
Outstanding at the end of the period (in shares)	71,892
2015 Plan
Stock Based Compensation Plans
Total shares reserved for issuance	1,679,793			1,900,000