Summary of Borrowed Funds (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Outstanding [Line Items]
FHLB advances	$ 13,234,500	$ 12,104,500
Repurchase agreements	200,000	450,000
Total wholesale borrowings	13,434,500	12,554,500
Junior subordinated debentures	359,339	359,179
Total borrowed funds	$ 13,793,839	$ 12,913,679