Common Stock (Performance Share Summary) (Details) - Performance Shares - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average per share grant date fair value per share of performance shares awarded		$ 38.11	$ 35.72	$ 26.36
Compensation expense	[1],[2]	$ 1,655	$ 1,042	$ 1,181
Deferred tax benefit related to compensation expense	[1]	$ 579	$ 365	$ 413

[1] Includes CEO retention grant.

[2] Includes adjustments for estimated forfeitures.