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Goodwill and Other Assets - Additional Information (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Goodwill and Intangible Assets Disclosure [Abstract] |  |  |
Goodwill | $ 2,776,188,000 us-gaap_Goodwill | $ 2,393,731,000 us-gaap_Goodwill |
Change in goodwill carrying amount | 382,500,000 us-gaap_GoodwillPeriodIncreaseDecrease | 228,100,000 us-gaap_GoodwillPeriodIncreaseDecrease |
Goodwill deductible for tax purpose | 229,300,000 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount |  |
Other intangible assets gross carrying amounts | 299,000,000 us-gaap_FiniteLivedIntangibleAssetsGross | 174,400,000 us-gaap_FiniteLivedIntangibleAssetsGross |
Accumulated amortization | 100,900,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization | 70,800,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization |
Amortization expense for existing other intangible assets | 30,100,000 us-gaap_AmortizationOfIntangibleAssets | 24,500,000 us-gaap_AmortizationOfIntangibleAssets | 15,000,000 us-gaap_AmortizationOfIntangibleAssets
Remaining weighted average amortization period of other intangible assets, in years | 8 years 8 months 12 days |  |
Weighted average amortization period includes amortization expense related to years beyond 2019 | 69,100,000 us-gaap_FiniteLivedIntangibleAssetsNet |  |
Other assets | 37,289,000 us-gaap_OtherAssetsMiscellaneousNoncurrent | 25,799,000 us-gaap_OtherAssetsMiscellaneousNoncurrent |
Carrying amount of cash surrender value of life insurance | 16,000,000 us-gaap_CashSurrenderValueOfLifeInsurance | 17,100,000 us-gaap_CashSurrenderValueOfLifeInsurance |
Investments in joint venture | $ 9,500,000 md_JointVentureInvestment |  |

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- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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- Definition The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479 + Details
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- Definition Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 17 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 4 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6812-107765 + Details
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- Definition Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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- Definition Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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- Definition Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 + Details
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- Definition Amount of increase (decrease) of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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- Definition Amount of other miscellaneous assets expected to be realized or consumed after one year or normal operating cycle, if longer. + References No definition available. + Details
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