Common Stock and Stock-based Compensation (Details 4) (Deferred Directors Compensation Plan [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred Directors Compensation Plan [Member]
Summary of stock activity for the directors deferred compensation plan
Number of options outstanding, Beginning Balance	101
Number of shares, Granted in Period	19
Number of options outstanding, Ending Balance	120	101
Directors' deferred compensation plan, weighted average grant date fair value
Restricted stock Options, Weighted Average Grant Date Fair Value, Beginning balance	$ 23.74
Number of restricted stock Options, Granted in Period, Weighted Average Grant Date Fair Value	$ 33.46	$ 26.99	$ 23.10
Restricted stock Options, Weighted Average Grant Date Fair Value, Ending balance	$ 25.33	$ 23.74