Accumulated Other Comprehensive Income - Summary of the Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amount reclassified from accumulated other comprehensive income
Net realized gains on investments, excluding other-than-temporary impairment losses	$ 165,122	$ 17,044	$ 16,365
Portion of net (gain) loss recognized in other comprehensive income, before taxes	206	(701)	(31)
Provision for income taxes	(206,243)	(41,013)	(34,999)
Net income	309,508	74,101	69,178
Reclassified from accumulated other comprehensive income
Amount reclassified from accumulated other comprehensive income
Net income	(96,617)	(2,846)	(8,997)
Unrealized gains on securities \| Reclassified from accumulated other comprehensive income
Amount reclassified from accumulated other comprehensive income
Net realized gains on investments, excluding other-than-temporary impairment losses	(147,965)	(5,203)	(13,866)
Provision for income taxes	51,788	1,821	4,853
Net income	(96,177)	(3,382)	(9,013)
OTTI \| Reclassified from accumulated other comprehensive income
Amount reclassified from accumulated other comprehensive income
Portion of net (gain) loss recognized in other comprehensive income, before taxes	(677)	824	24
Provision for income taxes	237	(288)	(8)
Net income	$ (440)	$ 536	$ 16

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (b)(7)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20187-122688

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=51831255

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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Amount before tax of other than temporary impairment (OTTI) on investment in available-for-sale debt security, recognized in other comprehensive loss, attributable to parent entity.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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