Capital Stock and Equity Awards - Commons Shares (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares outstanding	29,866,705	29,696,682
Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares issued during period	170,023
Common stock, shares outstanding	29,866,705	29,696,682	29,344,327	29,257,566
Options | Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares issued during period	127,196
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock unit dividend equivalents	$ 99		$ 77
Dividends payable	$ 409	$ 434
RSUs | Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares issued during period	42,827