Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	$ 5,770,731	$ 5,644,071
Total equity securities	32,585	30,551
Total securities	5,770,731	5,644,071
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	5,738,146	5,613,520
Total equity securities	32,585	30,551
Total securities	5,770,731	5,644,071
Fair Value, Measurements, Recurring | Preferred stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	15,353	13,846
Fair Value, Measurements, Recurring | Mutual Funds and Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	17,232	16,705
Fair Value, Measurements, Recurring | Mortgage-related Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	2,775,154	2,960,282
Fair Value, Measurements, Recurring | Mortgage-related Securities | GSE certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,315,836	1,707,521
Fair Value, Measurements, Recurring | Mortgage-related Securities | GSE CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,459,318	1,252,761
Fair Value, Measurements, Recurring | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	2,962,992	2,653,238
Fair Value, Measurements, Recurring | Other Securities | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	29,863
Fair Value, Measurements, Recurring | Other Securities | GSE debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,608,363	1,328,927
Fair Value, Measurements, Recurring | Other Securities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	864,957	821,715
Fair Value, Measurements, Recurring | Other Securities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	27,476	66,183
Fair Value, Measurements, Recurring | Other Securities | Capital trust notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	49,751	49,291
Fair Value, Measurements, Recurring | Other Securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	382,582	387,122
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	29,863
Total equity securities	15,353	13,846
Total securities	45,216	13,846
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Preferred stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	15,353	13,846
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	29,863
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Securities | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	29,863
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	5,708,283	5,613,520
Total equity securities	17,232	16,705
Total securities	5,725,515	5,630,225
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mutual Funds and Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	17,232	16,705
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-related Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	2,775,154	2,960,282
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-related Securities | GSE certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,315,836	1,707,521
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-related Securities | GSE CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,459,318	1,252,761
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	2,933,129	2,653,238
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | GSE debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,608,363	1,328,927
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	864,957	821,715
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	27,476	66,183
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | Capital trust notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	49,751	49,291
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	$ 382,582	$ 387,122