Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Statements of Cash Flows (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	[1]	$ 17,648	$ (19,103)	$ (564)
Investing activities:
Purchase of property and equipment		(43,176)	(56,757)	(81,842)
Proceeds from asset dispositions		14,245	1,296	14,983
Purchase of short-term investments		(284,481)	(637,980)	(321,453)
Proceeds from sale of short-term investments		334,488	862,942	316,543
Payments of deposits on aircraft		0	0	(2,249)
Loan to third party		0	(824)	0
Business acquisitions net of cash acquired		0	(126,644)	0
Loan to unconsolidated affiliate		(274)	0	(1,200)
Net cash provided by (used in) investing activities		20,802	42,033	(75,218)
Financing activities:
Debt issuance costs		(874)	0	0
Repurchase of common stock		(106)	(256)	(529)
Proceeds from line of credit		34,295	152,150	264,700
Payments on line of credit		(151,795)	(168,650)	(188,200)
Proceeds from related party term loan		130,000	0	0
Due to/from affiliate, net		0	0	0
Net cash provided by (used in) financing activities		11,520	(16,756)	75,971
Effect of exchange rate changes on cash and cash equivalents		(176)	0	0
Increase (decrease) in cash, cash equivalents and restricted cash		49,794	6,174	189
Cash, cash equivalents and restricted cash at beginning of period		8,770	2,596	2,407
Cash, cash equivalents and restricted cash at end of period		58,564	8,770	2,596
Parent Company Only (issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities				(46,738)
Investing activities:
Purchase of property and equipment				(81,484)
Proceeds from asset dispositions				14,983
Purchase of short-term investments				(321,453)
Proceeds from sale of short-term investments				316,543
Payments of deposits on aircraft				(2,249)
Loan to unconsolidated affiliate				(1,200)
Net cash provided by (used in) investing activities				(74,860)
Financing activities:
Repurchase of common stock				(529)
Proceeds from line of credit				264,700
Payments on line of credit				(188,200)
Due to/from affiliate, net				45,617
Net cash provided by (used in) financing activities				121,588
Increase (decrease) in cash, cash equivalents and restricted cash				(10)
Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities				52,873
Investing activities:
Net cash provided by (used in) investing activities				0
Financing activities:
Due to/from affiliate, net				(52,445)
Net cash provided by (used in) financing activities				(52,445)
Increase (decrease) in cash, cash equivalents and restricted cash				428
Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities				(6,699)
Investing activities:
Purchase of property and equipment				(358)
Net cash provided by (used in) investing activities				(358)
Financing activities:
Due to/from affiliate, net				6,828
Net cash provided by (used in) financing activities				6,828
Increase (decrease) in cash, cash equivalents and restricted cash				(229)
Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		0	0	0
Investing activities:
Net cash provided by (used in) investing activities		0	0	0
Financing activities:
Net cash provided by (used in) financing activities		0	0	0
Increase (decrease) in cash, cash equivalents and restricted cash		0	0	0
Cash, cash equivalents and restricted cash at beginning of period		0	0
Cash, cash equivalents and restricted cash at end of period		0	0	0
Reportable Legal Entities [Member] | Parent Company Only (issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		24,123	(62,581)
Investing activities:
Purchase of property and equipment		(40,865)	(56,757)
Proceeds from asset dispositions		14,245	1,296
Purchase of short-term investments		(284,481)	(637,980)
Proceeds from sale of short-term investments		334,488	862,942
Payments of deposits on aircraft			0
Loan to third party			(824)
Business acquisitions net of cash acquired			(130,788)
Loan to unconsolidated affiliate		(274)
Net cash provided by (used in) investing activities		23,113	37,889
Financing activities:
Debt issuance costs		(874)
Repurchase of common stock		(106)	(256)
Proceeds from line of credit		34,295	152,150
Payments on line of credit		(151,795)	(168,650)
Proceeds from related party term loan		130,000
Due to/from affiliate, net		(12,022)	41,459
Net cash provided by (used in) financing activities		(502)	24,703
Increase (decrease) in cash, cash equivalents and restricted cash		46,734	11
Cash, cash equivalents and restricted cash at beginning of period		47	36
Cash, cash equivalents and restricted cash at end of period		46,781	47	36
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		(16,952)	40,628
Investing activities:
Net cash provided by (used in) investing activities		0	0
Financing activities:
Due to/from affiliate, net		17,139	(41,656)
Net cash provided by (used in) financing activities		17,139	(41,656)
Increase (decrease) in cash, cash equivalents and restricted cash		187	(1,028)
Cash, cash equivalents and restricted cash at beginning of period		1,072	2,100
Cash, cash equivalents and restricted cash at end of period		1,259	1,072	2,100
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		10,477	2,850
Investing activities:
Purchase of property and equipment		(2,311)
Business acquisitions net of cash acquired			4,144
Net cash provided by (used in) investing activities		(2,311)	4,144
Financing activities:
Due to/from affiliate, net		(5,117)	197
Net cash provided by (used in) financing activities		(5,117)	197
Effect of exchange rate changes on cash and cash equivalents		(176)
Increase (decrease) in cash, cash equivalents and restricted cash		2,873	7,191
Cash, cash equivalents and restricted cash at beginning of period		7,651	460
Cash, cash equivalents and restricted cash at end of period		$ 10,524	$ 7,651	$ 460

[1] Net of the effect of business acquisitions.