Summary of Significant Accounting Policies - Impact of Revision (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Gain (loss) on revaluation of contingent consideration		$ (534)	$ (545)	$ (1,465)	$ 303
Operating income		3,371	5,808	12,478	17,659
Net income		1,191	5,791	9,555	17,765
Net income attributable to partners' capital		$ 144	4,132	$ 5,835	12,212
As Previously Reported [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Operating income			6,353		17,356
Net income			6,336		17,462
Net income attributable to partners' capital			4,458		12,029
Adjustments [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Gain (loss) on revaluation of contingent consideration	[1]		(545)		303
Operating income	[1]		(545)		303
Net income	[1]		(545)		303
Net income attributable to partners' capital	[1]		$ (326)		$ 183
Common Units [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Earnings per limited partner unit, basic and diluted		$ 0.00	$ 0.20	$ 0.27	$ 0.59
Common Units [Member] | As Previously Reported [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Earnings per limited partner unit, basic and diluted			0.22		0.58
Common Units [Member] | Adjustments [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Earnings per limited partner unit, basic and diluted	[1]		(0.02)		0.01
Subordinated Units [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Earnings per limited partner unit, basic and diluted			0.20		0.59
Subordinated Units [Member] | As Previously Reported [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Earnings per limited partner unit, basic and diluted			0.22		0.58
Subordinated Units [Member] | Adjustments [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Earnings per limited partner unit, basic and diluted	[1]		$ (0.02)		$ 0.01

[1] The corresponding amounts have been revised within the statement of cash flows for the nine months ended September 30, 2016, with no net impact to operating cash flow.