Company's derivative financial instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Liability			$ 0
Designated as Hedging Instrument [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative, Notional Amount	$ 2,000,000	$ 2,000,000
Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Asset
Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Liability
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative, Notional Amount	2,000,000	2,000,000
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Asset
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Liability