Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity Schedule of Accumulated Other Comprehensive Income (Loss) (Details)

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Stockholders' Equity Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Equity [Abstract]    
Unrealized gains $ 507,952 $ 475,694
Unrealized losses (542,885) (140,881)
Accumulated other comprehensive (loss) income $ (34,933) $ 334,813