Investments and Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Equity securities at fair value	$ 78,599	$ 91,977
Debt securities available for sale	91,204	83,445
Total investment securities at fair value	135,585	129,641
Long-term investment securities at fair value	34,218	45,781
Total	472,140
Liabilities:
Fair value of contingent liability	999
Total	999
Marketable equity securities
Assets:
Equity securities at fair value	21,155	23,819
Mutual funds invested in fixed income securities
Assets:
Equity securities at fair value	23,226	22,377
Equity securities
Assets:
Equity securities at fair value	44,381	46,196
U.S. Government securities
Assets:
Debt securities available for sale	19,200
Corporate securities
Assets:
Debt securities available for sale	52,434
U.S. mortgage-backed securities
Assets:
Debt securities available for sale	10,484
Commercial paper
Assets:
Debt securities available for sale	9,086
Fixed income securities
Assets:
Debt securities available for sale	91,204
Money market funds
Assets:
Cash and cash equivalents	255,294
Commercial paper
Assets:
Cash and cash equivalents	44,397
Certificates of deposit
Assets:
Cash and cash equivalents	2,111
Bonds
Assets:
Cash and cash equivalents	535
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total investment securities at fair value	44,381	46,196
Long-term investment securities at fair value	0	0
Total	300,210
Liabilities:
Fair value of contingent liability	0	0
Fair value of derivatives embedded within convertible debt		0
Total	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Marketable equity securities
Assets:
Equity securities at fair value	21,155	23,819
Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds invested in fixed income securities
Assets:
Equity securities at fair value	23,226	22,377
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Assets:
Equity securities at fair value	44,381	46,196
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government securities
Assets:
Debt securities available for sale	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate securities
Assets:
Debt securities available for sale	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. mortgage-backed securities
Assets:
Debt securities available for sale	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial paper
Assets:
Debt securities available for sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income securities
Assets:
Debt securities available for sale	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets:
Cash and cash equivalents	255,294
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial paper
Assets:
Cash and cash equivalents	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Certificates of deposit
Assets:
Cash and cash equivalents	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Bonds
Assets:
Cash and cash equivalents	535
Significant Other Observable Inputs (Level 2)
Assets:
Total investment securities at fair value	91,204	83,445
Long-term investment securities at fair value	0	0
Total	137,712
Liabilities:
Fair value of contingent liability	0	0
Fair value of derivatives embedded within convertible debt		0
Total	0
Significant Other Observable Inputs (Level 2) | Marketable equity securities
Assets:
Equity securities at fair value	0	0
Significant Other Observable Inputs (Level 2) | Mutual funds invested in fixed income securities
Assets:
Equity securities at fair value	0	0
Significant Other Observable Inputs (Level 2) | Equity securities
Assets:
Equity securities at fair value	0	0
Significant Other Observable Inputs (Level 2) | U.S. Government securities
Assets:
Debt securities available for sale	19,200
Significant Other Observable Inputs (Level 2) | Corporate securities
Assets:
Debt securities available for sale	52,434
Significant Other Observable Inputs (Level 2) | U.S. mortgage-backed securities
Assets:
Debt securities available for sale	10,484
Significant Other Observable Inputs (Level 2) | Commercial paper
Assets:
Debt securities available for sale	9,086	5,887
Significant Other Observable Inputs (Level 2) | Fixed income securities
Assets:
Debt securities available for sale	91,204
Significant Other Observable Inputs (Level 2) | Money market funds
Assets:
Cash and cash equivalents	0
Significant Other Observable Inputs (Level 2) | Commercial paper
Assets:
Cash and cash equivalents	44,397
Significant Other Observable Inputs (Level 2) | Certificates of deposit
Assets:
Cash and cash equivalents	2,111
Significant Other Observable Inputs (Level 2) | Bonds
Assets:
Cash and cash equivalents	0
Significant Unobservable Inputs (Level 3)
Assets:
Total investment securities at fair value	0	0
Long-term investment securities at fair value	0	0
Total	0
Liabilities:
Fair value of contingent liability	999	3,147
Fair value of derivatives embedded within convertible debt		4,999
Total	999
Significant Unobservable Inputs (Level 3) | Marketable equity securities
Assets:
Equity securities at fair value	0	0
Significant Unobservable Inputs (Level 3) | Mutual funds invested in fixed income securities
Assets:
Equity securities at fair value	0	0
Significant Unobservable Inputs (Level 3) | Equity securities
Assets:
Equity securities at fair value	0	0
Significant Unobservable Inputs (Level 3) | U.S. Government securities
Assets:
Debt securities available for sale	0
Significant Unobservable Inputs (Level 3) | Corporate securities
Assets:
Debt securities available for sale	0
Significant Unobservable Inputs (Level 3) | U.S. mortgage-backed securities
Assets:
Debt securities available for sale	0
Significant Unobservable Inputs (Level 3) | Commercial paper
Assets:
Debt securities available for sale	0	0
Significant Unobservable Inputs (Level 3) | Fixed income securities
Assets:
Debt securities available for sale	0
Significant Unobservable Inputs (Level 3) | Money market funds
Assets:
Cash and cash equivalents	0
Significant Unobservable Inputs (Level 3) | Commercial paper
Assets:
Cash and cash equivalents	0
Significant Unobservable Inputs (Level 3) | Certificates of deposit
Assets:
Cash and cash equivalents	0
Significant Unobservable Inputs (Level 3) | Bonds
Assets:
Cash and cash equivalents	0
Fair Value, Measurements, Recurring
Assets:
Total		533,133
Liabilities:
Fair value of contingent liability		3,147
Fair value of derivatives embedded within convertible debt		4,999
Total		8,146
Fair Value, Measurements, Recurring | Marketable equity securities
Assets:
Equity securities at fair value		23,819
Fair Value, Measurements, Recurring | Mutual funds invested in fixed income securities
Assets:
Equity securities at fair value		22,377
Fair Value, Measurements, Recurring | U.S. Government securities
Assets:
Debt securities available for sale		14,660
Fair Value, Measurements, Recurring | Corporate securities
Assets:
Debt securities available for sale		54,413
Fair Value, Measurements, Recurring | U.S. mortgage-backed securities
Assets:
Debt securities available for sale		6,816
Fair Value, Measurements, Recurring | Commercial paper
Assets:
Debt securities available for sale		5,887
Fair Value, Measurements, Recurring | Fixed income securities
Assets:
Debt securities available for sale		83,445
Fair Value, Measurements, Recurring | Index-linked U.S. bonds
Assets:
Debt securities available for sale		779
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities
Assets:
Debt securities available for sale		382
Fair Value, Measurements, Recurring | Foreign fixed-income securities
Assets:
Debt securities available for sale		508
Fair Value, Measurements, Recurring | Money market funds
Assets:
Cash and cash equivalents		307,655
Fair Value, Measurements, Recurring | Commercial paper
Assets:
Cash and cash equivalents		47,328
Fair Value, Measurements, Recurring | Certificates of deposit
Assets:
Cash and cash equivalents		2,193
Fair Value, Measurements, Recurring | Bonds
Assets:
Cash and cash equivalents		535
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total		354,386
Liabilities:
Total		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. mortgage-backed securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Index-linked U.S. bonds
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial mortgage-backed securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign fixed-income securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets:
Cash and cash equivalents		307,655
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial paper
Assets:
Cash and cash equivalents		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Certificates of deposit
Assets:
Cash and cash equivalents		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Bonds
Assets:
Cash and cash equivalents		535
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Total		132,966
Liabilities:
Total		0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Government securities
Assets:
Debt securities available for sale		14,660
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate securities
Assets:
Debt securities available for sale		54,413
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. mortgage-backed securities
Assets:
Debt securities available for sale		6,816
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Fixed income securities
Assets:
Debt securities available for sale		83,445
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Index-linked U.S. bonds
Assets:
Debt securities available for sale		779
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commercial mortgage-backed securities
Assets:
Debt securities available for sale		382
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign fixed-income securities
Assets:
Debt securities available for sale		508
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Money market funds
Assets:
Cash and cash equivalents		0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commercial paper
Assets:
Cash and cash equivalents		47,328
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Certificates of deposit
Assets:
Cash and cash equivalents		2,193
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Bonds
Assets:
Cash and cash equivalents		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Total		0
Liabilities:
Total		8,146
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. Government securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. mortgage-backed securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Fixed income securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Index-linked U.S. bonds
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Commercial mortgage-backed securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Foreign fixed-income securities
Assets:
Debt securities available for sale		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Money market funds
Assets:
Cash and cash equivalents		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Commercial paper
Assets:
Cash and cash equivalents		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Certificates of deposit
Assets:
Cash and cash equivalents		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Bonds
Assets:
Cash and cash equivalents		0
Current Restricted Assets | Fair Value, Measurements, Recurring | Commercial paper
Assets:
Cash and cash equivalents	10,374	4,423
Restricted Assets | Fair Value, Measurements, Recurring | Commercial paper
Assets:
Cash and cash equivalents	$ 1,907	$ 3,160