Investments - Amortized Costs and Estimated Fair Values (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale Securities [Abstract]
Amortized cost		$ 140,266
Unrealized gains		14
Unrealized losses		(78)
Estimated fair value		140,202
Cost Method Investments
Cost method investments, Gross unrealized gains	$ 0	0
Cost method investments, Gross unrealized losses	0	0
Total Investments
Amortized cost	9,285	148,225
Unrealized gains	0	14
Unrealized losses	0	(78)
Estimated fair value	9,285	148,161
U.S. treasury notes [Member]
Available-for-sale Securities [Abstract]
Amortized cost		17,609
Unrealized gains		1
Unrealized losses		(2)
Estimated fair value		17,608
Agency bonds [Member]
Available-for-sale Securities [Abstract]
Amortized cost		52,014
Unrealized gains		0
Unrealized losses		(63)
Estimated fair value		51,951
Commercial paper [Member]
Available-for-sale Securities [Abstract]
Amortized cost		13,500
Unrealized gains		0
Unrealized losses		0
Estimated fair value		13,500
Certificates of deposit [Member]
Available-for-sale Securities [Abstract]
Amortized cost		19,122
Unrealized gains		0
Unrealized losses		0
Estimated fair value		19,122
Municipal bonds [Member]
Available-for-sale Securities [Abstract]
Amortized cost		27,112
Unrealized gains		10
Unrealized losses		(3)
Estimated fair value		27,119
Corporate Bond Securities [Member]
Available-for-sale Securities [Abstract]
Amortized cost		10,909
Unrealized gains		3
Unrealized losses		(10)
Estimated fair value		10,902
Equity securities - mutual funds [Member]
Trading Securities [Abstract]
Amortized cost	8,677	7,351
Trading Securities, Gross Unrealized Gains	0	0
Trading Securities, Gross Unrealized Losses	0	0
Estimated fair value	8,677	7,351
Cost-method investments [Member]
Cost Method Investments
Amortized cost	608	608
Estimated fair value	$ 608	$ 608

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This item represents the gross unrealized losses for securities on cost method investments.

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This item represents the gross unrealized losses for investments held as of the balance sheet date.

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This item represents the amortized costs of all investments held as of the balance sheet date.

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This item represents the amortized cost of trading securities held as of the balance sheet date.

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This item represents the gross unrealized gains on trading securities held as of the balance sheet date.

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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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Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

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This item represents a financial instrument (as defined) for which it is not practicable to estimate fair value. Such disclosure may be for an individual financial instrument or a class of financial instruments.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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