Equity - Options (Details) - Stock options - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Nonqualified stock option activity
Outstanding, beginning of period	20,000	25,000	33,334
Granted (in shares)			0
Exercised (in shares)	(5,000)	(5,000)	(8,334)
Outstanding, end of period	15,000	20,000	25,000
Options exercisable at end of the period (in shares)	15,000	20,000	25,000
Weighted Average Price
Outstanding at the beginning of the year (in dollars per share)	$ 34.99	$ 32.92	$ 30.76
Exercised (in dollars per share)	24.65	24.65	24.31
Outstanding at the end of the year (in dollars per share)	38.43	34.99	32.92
Exercisable at the end of the period (in dollars per share)	$ 38.43	$ 34.99	$ 32.92
Other information
Aggregate intrinsic value of exercisable options at the end of the year	$ 95,000
Weighted average remaining contractual life of options exercisable	3 years 2 months 12 days	3 years 3 months 18 days	3 years 6 months
Value of options exercised	$ 123,000	$ 123,000	$ 202,000
Market value of options on the date of exercise	233,000	205,000	410,797
Compensation expense related to share-based award	$ 0	$ 0	$ 2,000