Condensed Parent Company Financial Statements - Schedule of Condensed Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
ASSETS
Cash and short-term investments	$ 128,170	$ 86,685	$ 94,002	$ 95,551
Securities available-for-sale, at fair value	1,241,176	1,403,069
Other assets	180,488	149,302
Total Assets	9,790,877	8,470,298
LIABILITIES
Junior subordinated debt owed to unconsolidated subsidiary trusts	137,559
Total Liabilities	8,449,469	7,348,166
SHAREHOLDERS' EQUITY	1,341,408	1,122,132	788,190	746,595
Total Liabilities and Shareholders' Equity	9,790,877	8,470,298
Parent Company [Member]
ASSETS
Cash and short-term investments	47,035	33,172	$ 61,732	$ 22,973
Investment in subsidiaries - Bank	1,404,565	1,175,005
Investment in subsidiaries - Nonbank	8,228	5,604
Securities available-for-sale, at fair value	2,133	1,891
Other assets	28,602	21,817
Total Assets	1,490,563	1,237,489
LIABILITIES
Junior subordinated debt owed to unconsolidated subsidiary trusts	137,559	106,196
Dividends payable and other liabilities	11,596	9,161
Total Liabilities	149,155	115,357
SHAREHOLDERS' EQUITY	1,341,408	1,122,132
Total Liabilities and Shareholders' Equity	$ 1,490,563	$ 1,237,489