New Accounting Pronouncements - Summary of Impact of Adopting New Accounting Standards on Consolidated Financial Statements (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	$ 245,639			$ 245,639			$ 188,300
Other current assets	200,633			200,633
Other non-current assets	763,852			763,852
Total assets	1,210,124			1,210,124			1,176,231
Accounts payable	80,823			80,823			51,375
Accrued personnel costs	42,750			42,750			45,264
Other current liabilities	181,839			181,839
Deferred income taxes, net	4,000			4,000			3,339
Other non-current liabilities	311,886			311,886
Total liabilities	621,298			621,298			645,352
Retained earnings	395,881			395,881			345,302
Other stockholders' equity	192,945			192,945
Total stockholders’ equity	588,826			588,826			530,879
Total liabilities and stockholders’ equity	1,210,124			1,210,124			1,176,231
Revenue	232,641	$ 232,641	$ 211,016	498,731	$ 452,475
Operating expenses	205,102		188,120	409,852	380,886
Gross margin	27,539		22,896	88,879	71,589
Corporate general and administrative expenses	9,993		9,232	20,021	18,000
Operating income (loss)	17,546		13,664	68,858	53,589
Other (expense) income:
Interest expense	(1,817)		(1,692)	(3,597)	(3,209)
Gain on sale of operations, net			23	663	45
Other income (expense), net	630		3,764	(599)	6,501
Total other (expense) income, net	(1,187)		2,095	(3,533)	3,337
Income from continuing operations before income tax expense	16,359		15,759	65,325	56,926
Income tax expense	3,238		4,343	16,394	20,484
Income from continuing operations	13,121		11,416	48,931	36,442
(Loss) gain from discontinued operations, net of tax	(15)		(418)	26	(570)
Net income	13,106		10,998	48,957	35,872
Cash flows from operating activities:
Net income	13,106		10,998	48,957	35,872
Adjustments to reconcile net income to net cash provided by operating activities:				18,908
Changes in assets and liabilities, net of acquisitions and divestitures:
Accounts receivable, net				(44,774)	(40,997)
Other assets				(4,955)	(263)
Accounts payable				18,796	14,376
Accrued personnel costs				(3,302)	(9,598)
Other liabilities				(2,617)	1,989
Other				10,245
Operating cash flows provide by continuing operations				41,258	24,778
Operating cash flows used in discontinued operations				(152)	(540)
Net cash provided by operating activities				41,106	24,238
Net provided by investing activities				42,471	31,757
Net cash used in financing activities				(75,530)	(51,284)
Net increase in cash, cash equivalents and restricted cash				8,047
Cash, cash equivalents and restricted cash at beginning of year		33,409		33,409	31,374
Cash, cash equivalents and restricted cash at end of period	41,456		$ 36,085	41,456	$ 36,085
Previously Reported [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net							188,300
Other current assets							259,873
Other non-current assets							728,058
Total assets							1,176,231
Accounts payable							51,375
Accrued personnel costs							45,264
Other current liabilities							237,607
Deferred income taxes, net							3,339
Other non-current liabilities							307,767
Total liabilities							645,352
Retained earnings							345,302
Other stockholders' equity							185,577
Total stockholders’ equity							530,879
Total liabilities and stockholders’ equity							1,176,231
Balances without Adoption of Topic 606 [Member] | Previously Reported [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	233,753			233,753
Other current assets	200,553			200,553
Other non-current assets	763,165			763,165
Total assets	1,197,471			1,197,471
Accounts payable	73,024			73,024
Accrued personnel costs	42,168			42,168
Other current liabilities	181,725			181,725
Deferred income taxes, net	3,130			3,130
Other non-current liabilities	310,933			310,933
Total liabilities	610,980			610,980
Retained earnings	393,546			393,546
Other stockholders' equity	192,945			192,945
Total stockholders’ equity	586,491			586,491
Total liabilities and stockholders’ equity	1,197,471			1,197,471
Revenue	232,158			497,750
Operating expenses	205,146			409,823
Gross margin	27,012			87,927
Corporate general and administrative expenses	9,993			20,021
Operating income (loss)	17,019			67,906
Other (expense) income:
Interest expense	(1,817)			(3,597)
Gain on sale of operations, net				663
Other income (expense), net	630			(599)
Total other (expense) income, net	(1,187)			(3,533)
Income from continuing operations before income tax expense	15,832			64,373
Income tax expense	3,113			16,155
Income from continuing operations	12,719			48,218
(Loss) gain from discontinued operations, net of tax	(15)			26
Net income	12,704			48,244
Cash flows from operating activities:
Net income	12,704			48,244
Adjustments to reconcile net income to net cash provided by operating activities:				18,908
Changes in assets and liabilities, net of acquisitions and divestitures:
Accounts receivable, net				(42,334)
Other assets				(4,996)
Accounts payable				17,278
Accrued personnel costs				(3,289)
Other liabilities				(2,798)
Other				10,245
Operating cash flows provide by continuing operations				41,258
Operating cash flows used in discontinued operations				(152)
Net cash provided by operating activities				41,106
Net provided by investing activities				42,471
Net cash used in financing activities				(75,530)
Net increase in cash, cash equivalents and restricted cash				8,047
Cash, cash equivalents and restricted cash at beginning of year		$ 33,409		33,409
Cash, cash equivalents and restricted cash at end of period	41,456			41,456
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net						$ 197,746
Other current assets						259,953
Other non-current assets						728,786
Total assets						1,186,485
Accounts payable						57,656
Accrued personnel costs						45,859
Other current liabilities						237,720
Deferred income taxes, net						3,970
Other non-current liabilities						308,779
Total liabilities						653,984
Retained earnings						346,924
Other stockholders' equity						185,577
Total stockholders’ equity						532,501	$ 532,501
Total liabilities and stockholders’ equity						1,186,485
Accounting Standards Update 2014-09 [Member] | Adjustments [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net						9,446
Other current assets						80
Other non-current assets						728
Total assets						10,254
Accounts payable						6,281
Accrued personnel costs						595
Other current liabilities						113
Deferred income taxes, net						631
Other non-current liabilities						1,012
Total liabilities						8,632
Retained earnings						1,622
Total stockholders’ equity						1,622
Total liabilities and stockholders’ equity						$ 10,254
Accounting Standards Update 2014-09 [Member] | Adjustments [Member] | Adjustments [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	(11,886)			(11,886)
Other current assets	(80)			(80)
Other non-current assets	(687)			(687)
Total assets	(12,653)			(12,653)
Accounts payable	(7,799)			(7,799)
Accrued personnel costs	(582)			(582)
Other current liabilities	(114)			(114)
Deferred income taxes, net	(870)			(870)
Other non-current liabilities	(953)			(953)
Total liabilities	(10,318)			(10,318)
Retained earnings	(2,335)			(2,335)
Total stockholders’ equity	(2,335)			(2,335)
Total liabilities and stockholders’ equity	(12,653)			(12,653)
Revenue	(483)			(981)
Operating expenses	44			(29)
Gross margin	(527)			(952)
Operating income (loss)	(527)			(952)
Other (expense) income:
Income from continuing operations before income tax expense	(527)			(952)
Income tax expense	(125)			(239)
Income from continuing operations	(402)			(713)
Net income	(402)			(713)
Cash flows from operating activities:
Net income	$ (402)			(713)
Changes in assets and liabilities, net of acquisitions and divestitures:
Accounts receivable, net				2,440
Other assets				(41)
Accounts payable				(1,518)
Accrued personnel costs				13
Other liabilities				$ (181)