Organization and Summary of Significant Accounting Policies, Unrealized Loss Position (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Net realized gains (losses) related to available-for-sale securities	$ 0	$ 0
Continuous unrealized loss position, fair value [Abstract]
In loss position less than 12 months	20,968	16,352
In loss position more than 12 months	7,945	6,765
Total in loss position	28,913	23,117
Continuous unrealized loss position, unrealized losses [Abstract]
In loss position less than 12 months	(37)	(16)
In loss position more than 12 months	(47)	(25)
Total in loss position	(84)	(41)
Certificates of Deposit [Member]
Continuous unrealized loss position, fair value [Abstract]
In loss position less than 12 months	718	480
In loss position more than 12 months	0	0
Total in loss position	718	480
Continuous unrealized loss position, unrealized losses [Abstract]
In loss position less than 12 months	(2)	0
In loss position more than 12 months	0	0
Total in loss position	(2)	0
Corporate Notes and Bonds [Member]
Continuous unrealized loss position, fair value [Abstract]
In loss position less than 12 months	16,530	12,450
In loss position more than 12 months	6,947	5,767
Total in loss position	23,477	18,217
Continuous unrealized loss position, unrealized losses [Abstract]
In loss position less than 12 months	(32)	(15)
In loss position more than 12 months	(47)	(25)
Total in loss position	(79)	(40)
U.S. Government Agency Securities [Member]
Continuous unrealized loss position, fair value [Abstract]
In loss position less than 12 months	3,720	3,422
In loss position more than 12 months	998	998
Total in loss position	4,718	4,420
Continuous unrealized loss position, unrealized losses [Abstract]
In loss position less than 12 months	(3)	(1)
In loss position more than 12 months	0	0
Total in loss position	$ (3)	$ (1)