Basis of Presentation and Summary of Significant Accounting Policies - Customer Who Represented 10% Or More Total Account Receivable (Detail) - Accounts Receivable, net - Customer Concentration Risk	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fresenius Medical Care Rx
Concentration Risk [Line Items]
Concentration risk percentage	29.00%	34.00%
AmerisourceBergen Drug Corporation
Concentration Risk [Line Items]
Concentration risk percentage	20.00%	20.00%
Cardinal Health, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	17.00%	25.00%
DaVita Rx
Concentration Risk [Line Items]
Concentration risk percentage	16.00%	0.00%
McKesson Corporation
Concentration Risk [Line Items]
Concentration risk percentage	14.00%	17.00%