Fair Value of Financial Instruments and Contingent Consideration - Carrying Value (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Liabilities:
Contingent consideration	$ 69,050,000	$ 76,700,000
Recurring
Other noncurrent assets
Marketable securities - restricted (SERP)	597,000	547,000
Total assets at fair value	849,928,000	773,439,000
Liabilities:
Contingent consideration	69,050,000	76,700,000
Total liabilities at fair value	69,050,000	76,700,000
Recurring \| Corporate debt securities
Marketable securities
Marketable securities	211,857,000	133,893,000
Long term marketable securities
Long term marketable securities	405,479,000	350,359,000
Recurring \| Municipal debt securities \| Total Fair Value
Marketable securities
Marketable securities	16,714,000
Recurring \| Cash
Assets:
Cash and cash equivalents	193,947,000	218,550,000
Recurring \| Money market funds
Assets:
Cash and cash equivalents	21,334,000	70,090,000
Recurring \| Level 1
Other noncurrent assets
Marketable securities - restricted (SERP)	5,000	3,000
Total assets at fair value	215,538,000	288,899,000
Liabilities:
Contingent consideration	0	0
Total liabilities at fair value	0	0
Recurring \| Level 1 \| Corporate debt securities
Marketable securities
Marketable securities	252,000	0
Long term marketable securities
Long term marketable securities	0	256,000
Recurring \| Level 1 \| Municipal debt securities
Marketable securities
Marketable securities	0
Recurring \| Level 1 \| Cash
Assets:
Cash and cash equivalents	193,947,000	218,550,000
Recurring \| Level 1 \| Money market funds
Assets:
Cash and cash equivalents	21,334,000	70,090,000
Recurring \| Level 2
Other noncurrent assets
Marketable securities - restricted (SERP)	592,000	544,000
Total assets at fair value	634,390,000	484,540,000
Liabilities:
Contingent consideration	0	0
Total liabilities at fair value	0	0
Recurring \| Level 2 \| Corporate debt securities
Marketable securities
Marketable securities	211,605,000	133,893,000
Long term marketable securities
Long term marketable securities	405,479,000	350,103,000
Recurring \| Level 2 \| Municipal debt securities
Marketable securities
Marketable securities	16,714,000
Recurring \| Level 2 \| Cash
Assets:
Cash and cash equivalents	0	0
Recurring \| Level 2 \| Money market funds
Assets:
Cash and cash equivalents	0	0
Recurring \| Level 3
Other noncurrent assets
Marketable securities - restricted (SERP)	0	0
Total assets at fair value	0	0
Liabilities:
Contingent consideration	69,050,000	76,700,000
Total liabilities at fair value	69,050,000	76,700,000
Recurring \| Level 3 \| Corporate debt securities
Marketable securities
Marketable securities	0	0
Long term marketable securities
Long term marketable securities	0	0
Recurring \| Level 3 \| Municipal debt securities
Marketable securities
Marketable securities
Recurring \| Level 3 \| Cash
Assets:
Cash and cash equivalents	0	0
Recurring \| Level 3 \| Money market funds
Assets:
Cash and cash equivalents	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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