Equity - Options (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Weighted Average Price
Outstanding at the beginning of the year (in dollars per share)	$ 29.60
Outstanding at the end of the year (in dollars per share)	$ 30.76	$ 29.60
Other information
Weighted average remaining contractual life (in years)	2 years 10 months 24 days	2 years 7 months 6 days
Stock options
Nonqualified stock option activity
Outstanding at the beginning of the year (in shares)	40,001	43,334
Granted (in shares)		0
Exercised (in shares)	(6,667)	(3,333)
Outstanding at the end of the year (in shares)	33,334	40,001
Options exercisable at end of the period (in shares)	28,334	30,001
Weighted Average Price
Outstanding at the beginning of the year (in dollars per share)	$ 29.60	$ 29.16
Exercised (in dollars per share)	23.79	23.79
Outstanding at the end of the year (in dollars per share)	30.76	29.60
Exercisable at the end of the period (in dollars per share)	$ 45.45	$ 31.99
Other information
Aggregate intrinsic value of exercisable options at the end of the year	$ 498,000
Weighted average remaining contractual life of options exercisable	2 years 10 months 24 days
Value of options exercised	$ 159,000	$ 79,000
Market value of options on the date of exercise	311,000	140,000
Compensation expense related to share-based award	$ 15,000	$ 14,000
Stock options | 2017
Other information
Awards scheduled to vest (in shares)	5,000
Remaining compensation expense	$ 3,000,000
Stock options | Vest beyond 2017
Other information
Awards scheduled to vest (in shares)	0