Share-Based Compensation Plan - Retainer Plan (Details) - Retainer Plan - Restricted stock awards - Non Employee Director - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 31, 2009
Share-Based Compensation
Available for future grant, at beginning	25,825	35,842
Retainer shares awarded	(13,144)	(10,017)
Plan Expiration	(12,681)
Available for future grant, at ending	0	25,825	35,842
Outstanding at beginning of period	154,175	144,158
Retainer shares awarded	13,144	10,017
Plan Expiration	12,681
Outstanding at end of period	167,319	154,175	144,158
Additional disclosures
Awards authorized				180,000
Compensation expense	$ 0.3	$ 0.3	$ 0.3