Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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-Publisher FASB
-Name Accounting Standards Codification
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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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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 losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

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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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Marketable Securities (Details) - USD ($) $ in Thousands	3 Months Ended
Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Recognized loss on sale of common stock included in interest and other income	$ 5,000
Estimated Fair Value	247,879		$ 276,928
Marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	249,646		276,567
Unrealized Loss	(1,767)
Unrealized Gain, Net			361
Estimated Fair Value	$ 247,879		$ 276,928
Accounting Standards Update 2016-01 \| Cumulative other comprehensive loss
Schedule of Available-for-sale Securities [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ (1,902)
Accounting Standards Update 2016-01 \| Cumulative net income
Schedule of Available-for-sale Securities [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ 1,902