Equity - Options (Details) - Stock options - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Nonqualified stock option activity
Outstanding, beginning of period	25,000	33,334	40,001
Granted (in shares)			0
Exercised (in shares)	(5,000)	(8,334)	(6,667)
Outstanding, end of period	20,000	25,000	33,334
Options exercisable at end of the period (in shares)	20,000	25,000	28,334
Weighted Average Price
Outstanding at the beginning of the year (in dollars per share)	$ 32.92	$ 30.76	$ 29.60
Exercised (in dollars per share)	24.65	24.31	23.79
Outstanding at the end of the year (in dollars per share)	34.99	32.92	30.76
Exercisable at the end of the period (in dollars per share)	$ 34.99	$ 32.92	$ 45.45
Other information
Aggregate intrinsic value of exercisable options at the end of the year	$ 134,000
Weighted average remaining contractual life of options exercisable	3 years 3 months 18 days	3 years 6 months	2 years 10 months 24 days
Value of options exercised	$ 123,000	$ 202,000	$ 159,000
Market value of options on the date of exercise	205,000	410,797	311,000
Compensation expense related to share-based award	$ 0	$ 2,000	$ 15,000