Stock-Based Compensation - Additional Information (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested share-based compensation arrangements granted \| $	$ 41.3
Period over which cost is expected to be recognized	2 years 7 months
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage payroll deduction that each employee may deduct	15.00%
Maximum shares (in shares)	200
Percentage of closing market price paid for purchase of whole shares	90.00%
Number of shares reserved (in shares)	1,800,000

Maximum percentage payroll deduction per employee per quarter.

No definition available.

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- Definition

Percentage of closing market price paid for purchase of common stock shares through employee stock purchase plan.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of reserved shares held by the Employee Stock Purchase Plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	bkd_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

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Data Type:	xbrli:durationItemType
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Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The highest quantity of shares an employee can purchase under the plan per period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

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