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Significant Accounting Policies (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Schedule of activity in the Graduation Fund    
Balance at beginning of year $ 9,706 $ 1,898
Revenue deferred 17,882 8,507
Benefit redeemed (6,651) (699)
Balance at end of year $ 20,937 $ 9,706