Accounts Payable, Accrued Expenses and Other Liabilities - Components of Other Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Liabilities Noncurrent [Abstract]
ROU liabilities	$ 228,620
Payroll taxes payable	15,825	$ 31,055
Accrued compensation	73,529	35,103
Business acquisition, contingent cash consideration	29,774	28,099
Credit enhancement deposit	25,000	25,000
Financial guarantee liability	45	32	$ 54
Deferred rent		49,334
Total	$ 372,793	$ 168,623