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Fair Value Measurements and Fair Value of Financial Instruments (Details) - Schedule of fair value on recurring item basis - Recurring [Member] - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Assets measured at fair value $ 413,467 $ 436,082
Municipal Securities [Member]    
Assets measured at fair value $ 9,505 $ 9,632
Unobservable Input
 Discount Rate
 Discount Rate
Range 2.90% 2.90%