Investments - Gains and proceeds (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments
Net realized gains on sale of investments	$ (973)
(Losses) gains on sale of investments		$ 10,750	$ 795
Proceeds from sale of available-for-sale debt securities	64,706	152,985	197,548
Proceeds from sale of available-for-sale securities		174,500
Maturities of investments - debt securities	10,000	13,988	185,000
Purchases of investments - debt securities	$ 6,995	94,791	$ 322,004
Purchases of available-for-sale securities		$ 115,900

Amount of realized gain (loss) on investment in debt and equity securities.

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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Amount of cash outflow to acquire investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of cash outflow for purchase of marketable security.

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Amount of cash inflow from maturity, prepayment and call of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (held-to-maturity or available-for-sale) during the period.

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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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