Employee Benefit Plans - Schedule of Weighted-Average Asset Allocation by Asset Category in Partnerships in Care Pension Plan (Detail) - Pension Plan [Member] - Partnership in Care Benefits Plan [Member]	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocation	0.70%	1.50%
Foreign Government Debt Securities [Member] | United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocation	19.00%	14.50%
Annuity Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocation	38.60%	41.60%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocation	29.40%	26.30%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocation	9.90%	12.10%
Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocation	2.40%	4.00%