Credit Agreements and Senior Notes - Summary of Carrying Value of Senior Notes, Net of Unamortized Discount and Debt Issuance Costs (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Senior Notes	$ 1,975,741	$ 1,973,922
3.45% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Senior Notes	248,759	248,455
7.875% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Senior Notes	491,655	490,491
5.70% Senior Notes due 2039 [Member]
Debt Instrument [Line Items]
Senior Notes	493,316	493,139
4.875% Senior Notes due 2043 [Member]
Debt Instrument [Line Items]
Senior Notes	$ 742,011	$ 741,837