Schedule of Fair Value and Carrying Value of Assets and Liabilities Recorded at Other Than Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value | Level 2
Assets
Assets, fair value disclosure	$ 67,924	$ 27,003
Liabilities
Long-term debt, including current maturities	467,500
Total liabilities	467,500
Fair Value | Level 3
Liabilities
Long-term debt, including current maturities		342,745
Total liabilities		342,745
Carrying Value
Assets
Assets, fair value disclosure	68,151	27,112
Liabilities
Long-term debt, including current maturities	500,000	342,312
Total liabilities	500,000	342,312
Money Market Funds | Fair Value | Level 2
Assets
Assets, fair value disclosure	28	61
Money Market Funds | Carrying Value
Assets
Assets, fair value disclosure	28	61
Commercial Paper | Fair Value | Level 2
Assets
Assets, fair value disclosure	64,290	25,322
Commercial Paper | Carrying Value
Assets
Assets, fair value disclosure	64,519	25,431
Corporate Bonds | Fair Value | Level 2
Assets
Assets, fair value disclosure	3,606	1,620
Corporate Bonds | Carrying Value
Assets
Assets, fair value disclosure	$ 3,604	$ 1,620