Business Segment, Geographic, and Concentration Risk Information - Summary of Customer Revenue and Accounts Receivable Concentration (Detail) - Commercial Platform and Global Supply Chain - Customer Concentration Risk	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Customer Revenue | Customer A
Concentration Risk [Line Items]
Concentration risk, percentage	27.00%		44.00%
Customer Revenue | Customer B
Concentration Risk [Line Items]
Concentration risk, percentage	13.00%	5.00%	9.00%	4.00%
Customer Revenue | Customer C
Concentration Risk [Line Items]
Concentration risk, percentage	12.00%	16.00%	13.00%	11.00%
Customer Revenue | Customer D
Concentration Risk [Line Items]
Concentration risk, percentage	11.00%	5.00%	8.00%	3.00%
Customer Revenue | Customer E
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%	7.00%	6.00%	11.00%
Customer Revenue | Customer F
Concentration Risk [Line Items]
Concentration risk, percentage	1.00%	18.00%	2.00%	20.00%
Accounts Receivable | Customer A
Concentration Risk [Line Items]
Concentration risk, percentage			27.00%		18.00%
Accounts Receivable | Customer B
Concentration Risk [Line Items]
Concentration risk, percentage			20.00%		10.00%
Accounts Receivable | Customer C
Concentration Risk [Line Items]
Concentration risk, percentage			13.00%		6.00%
Accounts Receivable | Customer D
Concentration Risk [Line Items]
Concentration risk, percentage			10.00%		4.00%
Accounts Receivable | Customer E
Concentration Risk [Line Items]
Concentration risk, percentage					26.00%
Accounts Receivable | Customer F
Concentration Risk [Line Items]
Concentration risk, percentage					13.00%