General - Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets
Investments	$ 433,248	$ 327,865
Cash held in bank accounts	30,300	114,700
Liabilities
Contingent consideration	9,120	8,817
U.S. Government and agency securities
Assets
Investments	52,716	28,231
Obligations of government-sponsored enterprises
Assets
Investments	13,026	22,088
Corporate debt securities
Assets
Investments	345,394	269,788
Taxable municipal bonds
Assets
Investments		5,000
Certificates of deposit
Assets
Investments	22,112	2,758
Level 1 \| 4.400% Senior Notes due 2024
Liabilities
Fair value of debt	389,200
Level 2 \| Term Loan
Liabilities
Fair value of debt	336,900
Fair value measured on recurring basis
Assets
Total assets held at fair value	649,091	611,929
Liabilities
Contingent consideration	9,120	8,817
Total liabilities held at fair value	9,120	8,817
Fair value measured on recurring basis \| Other than cash held in bank accounts by Company
Assets
Cash and cash equivalents	215,843	284,064
Fair value measured on recurring basis \| U.S. Government and agency securities
Assets
Investments	52,716	28,231
Fair value measured on recurring basis \| Obligations of government-sponsored enterprises
Assets
Investments	13,026	22,088
Fair value measured on recurring basis \| Corporate debt securities
Assets
Investments	345,394	269,788
Fair value measured on recurring basis \| Taxable municipal bonds
Assets
Investments		5,000
Fair value measured on recurring basis \| Certificates of deposit
Assets
Investments	22,112	2,758
Fair value measured on recurring basis \| Level 1
Assets
Total assets held at fair value	52,716	28,231
Fair value measured on recurring basis \| Level 1 \| U.S. Government and agency securities
Assets
Investments	52,716	28,231
Fair value measured on recurring basis \| Level 2
Assets
Total assets held at fair value	596,375	583,698
Fair value measured on recurring basis \| Level 2 \| Other than cash held in bank accounts by Company
Assets
Cash and cash equivalents	215,843	284,064
Fair value measured on recurring basis \| Level 2 \| Obligations of government-sponsored enterprises
Assets
Investments	13,026	22,088
Fair value measured on recurring basis \| Level 2 \| Corporate debt securities
Assets
Investments	345,394	269,788
Fair value measured on recurring basis \| Level 2 \| Taxable municipal bonds
Assets
Investments		5,000
Fair value measured on recurring basis \| Level 2 \| Certificates of deposit
Assets
Investments	22,112	2,758
Fair value measured on recurring basis \| Level 3
Liabilities
Contingent consideration	9,120	8,817
Total liabilities held at fair value	$ 9,120	$ 8,817

Fair value of contingent consideration in a business combination as of the balance sheet date.

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 5
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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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-Subparagraph (SX 210.5-02.1)
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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value of financial and nonfinancial obligations.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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