Represents the maturity periods of the investments held by the entity.

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Amount 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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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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No definition available.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of realized gain from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of realized loss from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of investment in equity security without readily determinable fair value.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Significant Accounting Policies - Equity Instruments and Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Equity Instruments and Investments
Equity instruments with readily determinable fair value	$ 84,100		$ 78,100
Cumulative effect adjustment					$ 7,264
Gain on sale of investment	3,800
Loss on sale of investment		$ 1,900
Equity instruments without readily determinable fair values	176,400		175,700
Debt securities of our captive insurance companies	$ 46,300		$ 40,100
Adjustment \| ASU 2016-01
Equity Instruments and Investments
Cumulative effect adjustment				$ 7,300
Debt Securities \| Securities in captive insurance subsidiary portfolio \| Minimum
Equity Instruments and Investments
Investment maturity period	1 year
Debt Securities \| Securities in captive insurance subsidiary portfolio \| Maximum
Equity Instruments and Investments
Investment maturity period	10 years