Significant Accounting Policies (Treasury Stock) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Treasury Stock
Equity, Class of Treasury Stock [Line Items]
Purchase of treasury shares, shares	0	111,292	412,473
Treasury Stock Acquired, Average Cost Per Share		$ 17.97	$ 37.03
Common Stock
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	941,250