Common Stock Summary of Changes in Common Stock (Details) - shares		1 Months Ended	12 Months Ended
	Nov. 16, 2016	Nov. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			28,630,000
Equity Issuance	1,012,000	880,000
Balance, end of period			28,630,000	28,630,000
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			28,630,000	27,427,000	27,284,000
Sales to shareholders under DRPP					46,000
Sales to employees under ESPP			18,000	18,000	19,000
Stock-based compensation			88,000	173,000	78,000
Equity Issuance				1,012,000
Balance, end of period			28,736,000	28,630,000	27,427,000