Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Purchase of common stock through tender offer, related costs			$ 200
Tax provision (benefit) on unrealized gain (loss) on investments	$ 11,000	$ 7,000	(6,000)
Accumulated Other Comprehensive (Loss) Income [Member]
Tax provision (benefit) on unrealized gain (loss) on investments	$ 11,000	$ 7,000	$ (6,000)

Amount of tax expense (benefit), after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities, attributable to parent entity. Excludes amounts related to other than temporary impairment (OTTI) loss.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
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