Short-Term Borrowings and Long-Term Debt - Outstanding Short Term Borrowings and Long Term Debt (Additional Information) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Debt Disclosure [Abstract]
Interest expense on debt	$ 8.6	$ 9.0	$ 17.0	$ 18.3
Weighted average interest rate on short-term borrowings	2.04%		2.04%		1.39%