Shareholders' Equity (Details) (Restricted Stock Units (RSUs) [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Restricted stock units under the 2006 and 2011 Incentive Plan [Abstract]
Maximum shares granted to employees (in shares)	700
Terms for stock vesting if earlier than five years	Each award vests at the end of five years from the date of grant, or at the time a recipient retires after reaching age 65, if earlier
Restricted Stock Units vested (in shares)	66	62
Shares withheld upon vesting (in shares)	14	20
Fair value of vested Restricted Stock Units	$ 2,785	$ 2,504
Compensation expense for 2006 and 2011 incentive plans	$ 301	$ 305
2006 Incentive Plan [Member]
Restricted stock units under the 2006 and 2011 Incentive Plan [Abstract]
Award vesting period	5 years
2011 Incentive Plan [Member]
Restricted stock units under the 2006 and 2011 Incentive Plan [Abstract]
Award vesting period	5 years