Consolidated Balance Sheets (Parenthetical) - USD ($) $ / shares in Thousands, $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Amortized Cost	$ 5,417,373	$ 4,997,529
Preferred Stock, No Par Value	$ 0	$ 0
Common Stock, No Par Value	$ 0	$ 0

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
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- Definition

Face amount per share of no-par value common stock.

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-Name Accounting Standards Codification
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-SubTopic 10
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Face amount per share of no-par value preferred stock nonredeemable or redeemable solely at the option of the issuer.

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