Statement of Consolidated Shareholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
At beginning and end of year	21,456,880	21,456,880	21,456,880
Dividends declared per share	$ 0.200	$ 0.200	$ 0.185
Shareholders' equity	$ 152,179	$ 141,539	$ 136,491
Common shares
At beginning and end of year	21,457,000	21,457,000	21,457,000	21,457,000
Shareholders' equity	$ 21,457	$ 21,457	$ 21,457	$ 21,457