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Stock-Based Compensation (Details) (USD $) | 12 Months Ended | 3 Months Ended |
--- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2011
Restricted stock awards [Roll Forward] |  |  |  |  |  |  |  |
Granted (in shares) | 1,662,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod | 1,328,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod | 1,592,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod |  |  |  |  |
Vested (in shares) | (1,185,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod | (1,455,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod | (1,435,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod |  |  |  |  |
Cancelled or forfeited (in shares) | (298,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod | (452,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod | (427,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod |  |  |  |  |
Ending balance (in shares) | 3,552,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber | 3,373,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber | 3,952,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber | 3,552,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber |  |  |  | 4,222,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Weighted Average Grant Date Fair Value [Roll Forward] |  |  |  |  |  |  |  |
Beginning balance (in dollars per share) | $ 21.12 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue | $ 16.67 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue | $ 14.93 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue |  |  |  | $ 21.12 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue |
Granted (in dollars per share) | $ 29.79 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue | $ 26.98 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue | $ 19.20 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue |  |  |  |  |
Vested (in dollars per share) | $ 19.58 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue | $ 15.08 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue | $ 14.28 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue |  |  |  |  |
Cancelled/forfeited (in dollars per share) | $ 21.02 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue | $ 18.87 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue | $ 15.62 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue |  |  |  |  |
Ending balance (in dollars per share) | $ 25.70 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue | $ 21.12 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue | $ 16.67 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue | $ 25.70 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue |  |  |  |
Unrecognized compensation cost related to nonvested share-based compensation arrangements granted | $ 59,100,000 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized |  |  | $ 59,100,000 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized |  |  |  |
Period over which cost is expected to be recognized | 2 years 3 months 18 days |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Restricted shares granted (in shares) | 1,662,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod | 1,328,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod | 1,592,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod |  |  |  |  |
Percentage of estimated forfeitures, minimum | 0.00%bkd_StockBasedCompensationPercentageOfEstimatedForfeituresMinimum |  |  |  |  |  |  |
Percentage of estimated forfeitures, maximum | 15.00%bkd_StockBasedCompensationPercentageOfEstimatedForfeituresMaximum |  |  |  |  |  |  |
Restricted Stock [Member] |  |  |  |  |  |  |  |
Restricted stock awards [Roll Forward] |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  | 32,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | 560,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | 42,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | 1,028,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Restricted shares granted (in shares) |  |  |  | 32,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | 560,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | 42,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | 1,028,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember |
Value per share minimum (in dollars per share) |  |  |  | $ 33.76 bkd_ShareBasedCompensationSharesAuthorizedUnderRestrictedStockPlansExercisePriceRangeLowerRangeLimit / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 33.42 bkd_ShareBasedCompensationSharesAuthorizedUnderRestrictedStockPlansExercisePriceRangeLowerRangeLimit / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 31.06 bkd_ShareBasedCompensationSharesAuthorizedUnderRestrictedStockPlansExercisePriceRangeLowerRangeLimit / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 27.01 bkd_ShareBasedCompensationSharesAuthorizedUnderRestrictedStockPlansExercisePriceRangeLowerRangeLimit / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember |
Value per share maximum (in dollars per share) |  |  |  | $ 33.76 bkd_ShareBasedCompensationSharesAuthorizedUnderRestrictedStockPlansExercisePriceRangeUpperRangeLimit / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 34.65 bkd_ShareBasedCompensationSharesAuthorizedUnderRestrictedStockPlansExercisePriceRangeUpperRangeLimit / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 33.84 bkd_ShareBasedCompensationSharesAuthorizedUnderRestrictedStockPlansExercisePriceRangeUpperRangeLimit / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 27.18 bkd_ShareBasedCompensationSharesAuthorizedUnderRestrictedStockPlansExercisePriceRangeUpperRangeLimit / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember |
Total value of restricted shares granted |  |  |  | $ 1,072,000 bkd_StockGrantedDuringPeriodValueRestrictedStockAward / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 19,356,000 bkd_StockGrantedDuringPeriodValueRestrictedStockAward / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 1,313,000 bkd_StockGrantedDuringPeriodValueRestrictedStockAward / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 27,774,000 bkd_StockGrantedDuringPeriodValueRestrictedStockAward / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember |
Employee Stock Purchase Plan [Member] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Percentage payroll deduction that each employee may deduct | 15.00%bkd_EligibleEmployeeMaximumQuarterlyContributionPercentageAllowed / us-gaap_AwardTypeAxis = bkd_EmployeeStockPurchasePlanMember |  |  |  |  |  |  |
Percentage of closing market price paid for purchase of whole shares | 90.00%bkd_PercentageOfCommonStockClosingMarketPriceToPurchaseWholeShares / us-gaap_AwardTypeAxis = bkd_EmployeeStockPurchasePlanMember |  |  |  |  |  |  |
Number of shares reserved (in shares) | 1,800,000 bkd_SharesHeldInEmployeeStockPurchasePlanReserved / us-gaap_AwardTypeAxis = bkd_EmployeeStockPurchasePlanMember |  |  | 1,800,000 bkd_SharesHeldInEmployeeStockPurchasePlanReserved / us-gaap_AwardTypeAxis = bkd_EmployeeStockPurchasePlanMember |  |  |  |

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- Definition The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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