Derivative Financial Instruments - Information about Hedged Items Included in Consolidated Balance Sheet (Detail) - Long-term Debt [Member] - Derivatives Designated and Qualifying as Hedging Instruments [Member] - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Carrying Amount [Member]
Derivatives, Fair Value [Line Items]
Hedged Item	$ 4,428,645	$ 4,394,109
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Derivatives, Fair Value [Line Items]
Hedged Item	$ (17,088)	$ (51,102)