Common Stock Summary of Changes in Common Stock (Details) - shares		1 Months Ended	12 Months Ended
	Nov. 16, 2016	Nov. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			27,427,000
Equity Issuance	1,012,000	880,000
Balance, end of period			28,630,000	27,427,000
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			27,427,000	27,284,000	27,075,000
Sales to shareholders under DRPP				46,000	102,000
Sales to employees under ESPP			18,000	19,000	24,000
Stock-based compensation			173,000	78,000	83,000
Equity Issuance			1,012,000
Balance, end of period			28,630,000	27,427,000	27,284,000