Amount of amortization expense attributable to debt issuance costs.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(8))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(8))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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

Commitments and Contingencies - Contingent Consideration (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Contingent consideration
Non-cash interest related to contingent liabilities	$ 602	$ 684	$ 409
Accrued incentives and earn-outs	8,916	12,229
Real Estate Investment \| Accrued incentives and earn-out liabilities
Contingent consideration
Non-cash interest related to contingent liabilities	602
Fair Value \| Level 3
Contingent consideration
Accrued incentives and earn-outs	8,916	$ 12,229
Fair Value \| Real Estate Investment \| Accrued incentives and earn-out liabilities
Contingent consideration
Accrued incentives and earn-outs	$ 8,916