New Accounting Pronouncements - Summary of Cumulative Effect of Changes Made to Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	$ 234,906		$ 188,300
Other current assets	188,931
Other non-current assets	766,019
Total assets	1,189,856		1,176,231
Accounts payable	57,764		51,375
Accrued personnel costs	55,038		45,264
Other current liabilities	168,995
Deferred income taxes, net	5,636		3,339
Other non-current liabilities	300,508
Total liabilities	587,941		645,352
Retained earnings	409,467		345,302
Other stockholders' equity	192,448
Total stockholders’ equity	601,915		530,879
Total liabilities and stockholders’ equity	$ 1,189,856		1,176,231
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
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