Parent Company Financial Statements - Statements of Income of Parent Company Only (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Dividend income from subsidiaries	$ 39	$ 228	$ 103
Interest income	546,795	508,983	440,386
Other income	117	94	129
Interest expense	48,573	42,686	44,344
Income tax benefit	(69,993)	(62,620)	(44,756)
Net Income	159,649	144,050	117,804
Parent Company [Member]
Dividend income from subsidiaries	95,443	94,900	83,103
Interest income	4,845	4,856	5,277
Equity in undistributed income (loss) of subsidiaries	71,739	55,631	43,804
Other income	1,053	1,920	1,874
Total Income	101,341	101,676	90,254
Interest expense	9,526	8,503	14,325
Other expenses	8,993	9,252	8,196
Total Expenses	18,519	17,755	22,521
Income Before Taxes and Equity in Undistributed Income of Subsidiaries	82,822	83,921	67,733
Income tax benefit	5,088	4,498	6,267
Income after income taxes	87,910	88,419	74,000
Net Income	159,649	144,050	117,804
Parent Company [Member] | Bank [Member]
Dividend income from subsidiaries	87,580	85,000	77,153
Equity in undistributed income (loss) of subsidiaries	71,581	55,742	42,094
Parent Company [Member] | Non-Bank [Member]
Dividend income from subsidiaries	7,863	9,900	5,950
Equity in undistributed income (loss) of subsidiaries	$ 158	$ (111)	$ 1,710