Fair Value Measurements (Narrative) (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total credit-related financial instruments with off-balance sheet risk	$ 5,391,027	$ 5,399,762
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book value of other real estate owned (OREO) and repossessed assets	4,000
Rabbi Trust [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	2,900
Alternative investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	16,500
Total credit-related financial instruments with off-balance sheet risk	$ 9,100