Common Stock (Details) - USD ($) $ in Thousands	12 Months Ended			192 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2012
Stockholders' Equity Note [Abstract]
Common Stock Shares Authorized	100,000,000	100,000,000		100,000,000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserved Shares Dividend Reinvestment and Direct Stock Purchase Plan	297,879			297,879
Stock Transactions, Parenthetical Disclosures [Abstract]
Balance, beginning of period	27,284,000
Balance, end of period	27,427,000	27,284,000		27,427,000
Stock Repurchase Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program Expiration Date	May 31, 2016
Stock Repurchase Program, Number of Shares Authorized to be Repurchased	2,800,000			2,800,000
Stock Repurchase Program, Authorized Amount	$ 100,000			$ 100,000
Treasury Stock, Shares, Acquired	0			2,100,000
Treasury Stock Program				$ 83,300
Employee Stock Purchase Plan Member [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserved Shares Employee Stock Purchase Plan	78,857			78,857
Restated Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding	352,688	416,088	492,150	352,688	529,925
Common Stock [Member]
Stock Transactions, Parenthetical Disclosures [Abstract]
Balance, beginning of period	27,284,000	27,075,000	26,917,000
Sales to Employees Under ESPP	19,000	24,000	16,000
Stock-based compensation	78,000	83,000	42,000
Sales to shareholders under DRPP	46,000	102,000	100,000
Balance, end of period	27,427,000	27,284,000	27,075,000	27,427,000