Parent Company Information - Schedule of Condensed Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Available for sale	$ 1,749,544	$ 1,493,905
Other assets	659,721	542,839
Total Assets	31,863,088	24,002,306
Liabilities and Shareholders’ Equity
Long-term borrowings	1,654,268	2,315,819
Junior subordinated debentures issued to capital trusts	55,370	41,774
Shareholders’ equity	3,350,454	2,533,165	$ 2,377,156	$ 2,207,091
Total Liabilities and Shareholders’ Equity	31,863,088	24,002,306
Parent Company
Assets
Cash	109,839	90,807
Available for sale	0	254
Investments in and receivables due from subsidiaries	3,609,836	2,738,700
Other assets	32,721	36,277
Total Assets	3,752,396	2,866,038
Liabilities and Shareholders’ Equity
Dividends payable to shareholders	37,644	33,100
Long-term borrowings	294,602	235,153
Junior subordinated debentures issued to capital trusts	55,370	41,774
Accrued expenses and other liabilities	14,326	22,846
Shareholders’ equity	3,350,454	2,533,165
Total Liabilities and Shareholders’ Equity	$ 3,752,396	$ 2,866,038