New Accounting Pronouncements - Summary of Impact of Adopting New Accounting Standards on Consolidated Financial Statements (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	$ 261,336			$ 188,300
Other current assets	202,226
Other non-current assets	750,791
Total assets	1,214,353			1,176,231
Accounts payable	63,157			51,375
Accrued personnel costs	30,790			45,264
Other current liabilities	194,394
Deferred income taxes, net	2,791			3,339
Other non-current liabilities	351,605
Total liabilities	642,737			645,352
Retained earnings	382,775			345,302
Other stockholders' equity	188,841
Total stockholders’ equity	571,616			530,879
Total liabilities and stockholders’ equity	1,214,353			1,176,231
Revenue	266,090	$ 241,459
Operating expenses	204,750	192,766
Gross margin	61,340	48,693
Corporate general and administrative expenses	10,028	8,768
Operating income	51,312	39,925
Other (expense) income:
Interest expense	(1,780)	(1,517)
Gain on sale of operations, net	663	22
Other expense, net	(1,229)	2,737
Total other (expense) income, net	(2,346)	1,242
Income from continuing operations before income tax expense	48,966	41,167
Income tax expense	13,156	16,141
Income from continuing operations	35,810	25,026
Gain (loss) from discontinued operations, net of tax	41	(152)
Net income	35,851	24,874
Cash flows from operating activities:
Net income	35,851	24,874
Adjustments to reconcile net income to net cash provided by operating activities:	7,906
Changes in assets and liabilities, net of acquisitions and divestitures:
Accounts receivable, net	(64,111)	(46,077)
Other assets	(2,571)	1,088
Accounts payable	5,501	1,285
Accrued personnel costs	(15,262)	(18,800)
Other liabilities	(3,366)	(1,767)
Other	15,413
Operating cash flows used in continuing operations	(20,639)	(14,374)
Operating cash flows provided by (used in) discontinued operations	139	(118)
Net cash used in operating activities	(20,500)	(14,492)
Net provided by investing activities	37,455	48,847
Net cash used in financing activities	(20,296)	(36,654)
Net decrease in cash, cash equivalents and restricted cash	(3,341)
Cash, cash equivalents and restricted cash at beginning of year	33,409	31,374
Cash, cash equivalents and restricted cash at end of period	30,068	$ 29,075
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	248,713
Other current assets	202,146
Other non-current assets	750,084
Total assets	1,200,943
Accounts payable	54,167
Accrued personnel costs	30,144
Other current liabilities	194,279
Deferred income taxes, net	2,046
Other non-current liabilities	350,624
Total liabilities	631,260
Retained earnings	380,842
Other stockholders' equity	188,841
Total stockholders’ equity	569,683
Total liabilities and stockholders’ equity	1,200,943
Revenue	265,592
Operating expenses	204,677
Gross margin	60,915
Corporate general and administrative expenses	10,028
Operating income	50,887
Other (expense) income:
Interest expense	(1,780)
Gain on sale of operations, net	663
Other expense, net	(1,229)
Total other (expense) income, net	(2,346)
Income from continuing operations before income tax expense	48,541
Income tax expense	13,042
Income from continuing operations	35,499
Gain (loss) from discontinued operations, net of tax	41
Net income	35,540
Cash flows from operating activities:
Net income	35,540
Adjustments to reconcile net income to net cash provided by operating activities:	7,906
Changes in assets and liabilities, net of acquisitions and divestitures:
Accounts receivable, net	(60,934)
Other assets	(2,593)
Accounts payable	2,793
Accrued personnel costs	(15,313)
Other liabilities	(3,451)
Other	15,413
Operating cash flows used in continuing operations	(20,639)
Operating cash flows provided by (used in) discontinued operations	139
Net cash used in operating activities	(20,500)
Net provided by investing activities	37,455
Net cash used in financing activities	(20,296)
Net decrease in cash, cash equivalents and restricted cash	(3,341)
Cash, cash equivalents and restricted cash at beginning of year	33,409
Cash, cash equivalents and restricted cash at end of period	30,068
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	12,623
Other current assets	80
Other non-current assets	707
Total assets	13,410
Accounts payable	8,990
Accrued personnel costs	646
Other current liabilities	115
Deferred income taxes, net	745
Other non-current liabilities	981
Total liabilities	11,477
Retained earnings	1,933
Total stockholders’ equity	1,933
Total liabilities and stockholders’ equity	13,410
Revenue	(498)
Operating expenses	(73)
Gross margin	(425)
Operating income	(425)
Other (expense) income:
Income from continuing operations before income tax expense	(425)
Income tax expense	(114)
Income from continuing operations	(311)
Net income	(311)
Cash flows from operating activities:
Net income	(311)
Changes in assets and liabilities, net of acquisitions and divestitures:
Accounts receivable, net	3,177
Other assets	(22)
Accounts payable	(2,708)
Accrued personnel costs	(51)
Other liabilities	$ (85)