Basis of Presentation and Significant Accounting Policies - Summary of Impact of Adopting New Accounting Standards on Consolidated Financial Statements (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Dec. 31, 2015
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	$ 207,287				$ 188,300				$ 207,287	$ 188,300
Other current assets	216,251				259,873				216,251	259,873
Other non-current assets	759,493				728,058				759,493	728,058
Total assets	1,183,031				1,176,231				1,183,031	1,176,231
Accounts payable	58,630				51,375				58,630	51,375
Accrued personnel costs	63,953				45,264				63,953	45,264
Other current liabilities	198,731				237,607				198,731	237,607
Deferred income taxes, net	6,764				3,339				6,764	3,339
Other non-current liabilities	261,290				307,767				261,290	307,767
Total liabilities	589,368				645,352				589,368	645,352
Retained earnings	408,963				345,302				408,963	345,302
Other stockholders' equity	184,700				185,577				184,700	185,577
Total stockholders’ equity	593,663				530,879				593,663	530,879	$ 480,021		$ 427,948
Total liabilities and stockholders’ equity	1,183,031				1,176,231				1,183,031	1,176,231
Revenue									922,003	855,340	799,832
Operating expenses	181,824	$ 198,607	$ 205,102	$ 204,750	189,975	$ 184,723	$ 188,120	$ 192,766	790,283	755,584	697,726
Gross margin	17,199	25,642	27,539	61,340	5,167	23,000	22,896	48,693	131,720	99,756	102,106
Corporate general and administrative expenses	8,873	10,279	9,993	10,028	7,316	7,979	9,232	8,768	39,173	33,295	36,319
Operating income (loss)	8,326	15,363	17,546	51,312	(2,149)	15,021	13,664	39,925	92,547	66,461	65,787
Other (expense) income:
Interest expense	(1,434)	(1,614)	(1,817)	(1,780)	(1,689)	(1,777)	(1,692)	(1,517)	(6,645)	(6,675)	(6,593)
Gain on sale of operations, net	362			663			23	22	1,025	45	855
Other expense, net	(9,631)	3,143	630	(1,229)	5,196	2,792	3,764	2,737	(7,087)	14,489	6,957
Total other (expense) income, net	(10,703)	1,529	(1,187)	(2,346)	3,507	1,015	2,095	1,242	(12,707)	7,859	1,219
Income from continuing operations before income tax expense	(2,377)	16,892	16,359	48,966	1,358	16,036	15,759	41,167	79,840	74,320	67,006
Income tax expense	(1,424)	3,297	3,238	13,156	(3,368)	6,172	4,343	16,141	18,267	23,288	26,399
Income (loss) from continuing operations	(953)	13,595	13,121	35,810	4,726	9,864	11,416	25,026	61,573	51,032	40,607
Loss from operations of discontinued operations, net of tax	(20)	(9)	(15)	41	121	(206)	(418)	(152)	(3)	(655)	(542)
Net income (loss)	(973)	13,586	13,106	35,851	4,847	9,658	10,998	24,874	61,570	50,377	40,065
Cash flows from operating activities:
Net income	(973)	$ 13,586	$ 13,106	35,851	4,847	$ 9,658	$ 10,998	24,874	61,570	50,377	40,065
Adjustments to reconcile net income to net cash provided by operating activities:									38,713
Changes in assets and liabilities, net of acquisitions and divestitures:
Accounts receivable, net									(10,668)	(13,849)	(19,188)
Other assets									(3,344)	3,180	(5,612)
Accounts payable									974	3,738	10,217
Accrued personnel costs									17,901	(599)	5,496
Other liabilities									(140)	3,508	5,965
Other									426
Net cash provided by continuing operations									105,432	77,663	73,674
Operating cash flows used in discontinued operations									(184)	(627)	387
Net cash provided by operating activities									105,248	77,036	74,061
Net provided by investing activities									(47,576)	(48,681)	(9,847)
Net cash used in financing activities									(109,380)	(45,593)	(18,384)
Net increase in cash, cash equivalents and restricted cash									(51,708)
Cash, cash equivalents and restricted cash at beginning of year				182,262				$ 199,500	182,262	199,500	153,670
Cash, cash equivalents and restricted cash at end of year	130,554				182,262				130,554	182,262	$ 199,500
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net												$ 198,398
Other current assets												259,953
Other non-current assets												728,786
Total assets												1,187,137
Accounts payable												57,656
Accrued personnel costs												45,859
Other current liabilities												237,720
Deferred income taxes, net												4,153
Other non-current liabilities												308,779
Total liabilities												654,167
Retained earnings												347,393
Other stockholders' equity												185,577
Total stockholders’ equity												532,970
Total liabilities and stockholders’ equity												1,187,137
Accounting Standards Update 2014-09 [Member] | Adjustments [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	(12,671)								(12,671)			10,098
Other current assets	(80)								(80)			80
Other non-current assets	(647)								(647)			728
Total assets	(13,398)								(13,398)			10,906
Accounts payable	(7,930)								(7,930)			6,281
Accrued personnel costs	(587)								(587)			595
Other current liabilities	(113)								(113)			113
Deferred income taxes, net	(1,035)								(1,035)			814
Other non-current liabilities	(897)								(897)			1,012
Total liabilities	(10,562)								(10,562)			8,815
Retained earnings	(2,836)								(2,836)			2,091
Total stockholders’ equity	(2,836)								(2,836)			2,091
Total liabilities and stockholders’ equity	(13,398)								(13,398)			$ 10,906
Revenue									(1,039)
Operating expenses									(73)
Gross margin									(966)
Operating income (loss)									(966)
Other (expense) income:
Income from continuing operations before income tax expense									(966)
Income tax expense									(221)
Income (loss) from continuing operations									(745)
Net income (loss)									(745)
Cash flows from operating activities:
Net income									(745)
Changes in assets and liabilities, net of acquisitions and divestitures:
Accounts receivable, net									2,573
Other assets									(81)
Accounts payable									(1,649)
Accrued personnel costs									8
Other liabilities									(106)
Accounting Standards Update 2014-09 [Member] | Balances without Adoption of Topic 606 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	194,616								194,616
Other current assets	216,171								216,171
Other non-current assets	758,846								758,846
Total assets	1,169,633								1,169,633
Accounts payable	50,700								50,700
Accrued personnel costs	63,366								63,366
Other current liabilities	198,618								198,618
Deferred income taxes, net	5,729								5,729
Other non-current liabilities	260,393								260,393
Total liabilities	578,806								578,806
Retained earnings	406,127								406,127
Other stockholders' equity	184,700								184,700
Total stockholders’ equity	590,827								590,827
Total liabilities and stockholders’ equity	1,169,633								1,169,633
Revenue									920,964
Operating expenses									790,210
Gross margin									130,754
Corporate general and administrative expenses									39,173
Operating income (loss)									91,581
Other (expense) income:
Interest expense									(6,645)
Gain on sale of operations, net									1,025
Other expense, net									(7,087)
Total other (expense) income, net									(12,707)
Income from continuing operations before income tax expense									78,874
Income tax expense									18,046
Income (loss) from continuing operations									60,828
Loss from operations of discontinued operations, net of tax									(3)
Net income (loss)									60,825
Cash flows from operating activities:
Net income									60,825
Adjustments to reconcile net income to net cash provided by operating activities:									38,713
Changes in assets and liabilities, net of acquisitions and divestitures:
Accounts receivable, net									(8,095)
Other assets									(3,425)
Accounts payable									(675)
Accrued personnel costs									17,909
Other liabilities									(246)
Other									426
Net cash provided by continuing operations									105,432
Operating cash flows used in discontinued operations									(184)
Net cash provided by operating activities									105,248
Net provided by investing activities									(47,576)
Net cash used in financing activities									(109,380)
Net increase in cash, cash equivalents and restricted cash									(51,708)
Cash, cash equivalents and restricted cash at beginning of year				$ 182,262					182,262
Cash, cash equivalents and restricted cash at end of year	$ 130,554				$ 182,262				$ 130,554	$ 182,262