Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Statements of Cash Flows (Detail) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	$ (23,677)	$ 5,410
Investing activities:
Purchase of property and equipment	(8,970)	(18,098)
Proceeds from asset dispositions	1,235	1,453
Purchase of short-term investments	(183,421)	(260,996)
Proceeds from sale of short-term investments	121,512	264,918
Payment of deposit on aircraft	(50)	0
Refund of deposit on aircraft	503	0
Loan to unconsolidated affiliate		(274)
Net cash used in investing activities	(69,191)	(12,997)
Financing activities:
Debt issuance cost	(5,668)	0
Proceeds from Term Loan	70,000	0
Proceeds from line of credit		34,295
Payments on line of credit		(29,575)
Repurchase of common stock		(51)
Net cash provided by financing activities	64,332	4,669
Effect of exchange rate changes on cash	(483)	0
Decrease in cash, cash equivalents and restricted cash	(29,019)	(2,918)
Cash, cash equivalents and restricted cash at the beginning of period	58,564	8,770
Cash, cash equivalents and restricted cash at end of period	29,545	5,852
Reportable Legal Entities [Member] \| Parent Company Only (issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	(20,773)	(506)
Investing activities:
Purchase of property and equipment	(5,956)	(16,768)
Proceeds from asset dispositions	1,235	1,453
Purchase of short-term investments	(183,421)	(260,996)
Proceeds from sale of short-term investments	121,512	264,918
Payment of deposit on aircraft	(50)
Refund of deposit on aircraft	503
Loan to unconsolidated affiliate		(274)
Net cash used in investing activities	(66,177)	(11,667)
Financing activities:
Debt issuance cost	(5,668)
Proceeds from Term Loan	70,000
Proceeds from line of credit		34,295
Payments on line of credit		(29,575)
Due to/from affiliate, net	(8,330)	7,510
Repurchase of common stock		(51)
Net cash provided by financing activities	56,002	12,179
Decrease in cash, cash equivalents and restricted cash	(30,948)	6
Cash, cash equivalents and restricted cash at the beginning of period	46,781	47
Cash, cash equivalents and restricted cash at end of period	15,833	53
Reportable Legal Entities [Member] \| Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	(6,064)	3,306
Financing activities:
Due to/from affiliate, net	7,028	(3,073)
Net cash provided by financing activities	7,028	(3,073)
Decrease in cash, cash equivalents and restricted cash	964	233
Cash, cash equivalents and restricted cash at the beginning of period	1,259	1,072
Cash, cash equivalents and restricted cash at end of period	2,223	1,305
Reportable Legal Entities [Member] \| Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	3,160	2,610
Investing activities:
Purchase of property and equipment	(3,014)	(1,330)
Net cash used in investing activities	(3,014)	(1,330)
Financing activities:
Due to/from affiliate, net	1,302	(4,437)
Net cash provided by financing activities	1,302	(4,437)
Effect of exchange rate changes on cash	(483)
Decrease in cash, cash equivalents and restricted cash	965	(3,157)
Cash, cash equivalents and restricted cash at the beginning of period	10,524	7,651
Cash, cash equivalents and restricted cash at end of period	$ 11,489	$ 4,494

Payments for deposits for purchase of productive assets.

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Proceeds from refund on deposit on aircraft.

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Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of increase (decrease) from the effect of exchange rate changes on cash and cash equivalent balances held in foreign currencies.

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Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

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Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

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The cash outflow to reacquire common stock during the period.

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