PARENT COMPANY FINANCIAL INFORMATION (Statements of Condition) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets
Cash and cash equivalents	$ 134,125	$ 72,882
Investments available-for-sale (at fair value)	733,554	592,049
Investments held-to-maturity	0	208,265
Other assets	124,137	117,208
Total assets	5,091,383	4,655,380	$ 4,397,132
Liabilities
Subordinated debentures	30,000	35,000
Accrued expenses and other liabilities	35,148	38,078
Total liabilities	4,557,811	4,130,953
Stockholders Equity
Common stock	23,901	24,296
Additional paid in capital	165,871	175,588
Retained earnings	350,414	325,840
Accumulated other comprehensive income (loss)	(6,614)	(1,297)	(823)	$ (2,970)
Total stockholders equity	533,572	524,427	$ 521,751	$ 499,363
Total liabilities and stockholders equity	5,091,383	4,655,380
Parent Company [Member]
Assets
Cash and cash equivalents	10,869	9,154
Investments available-for-sale (at fair value)	10,357	1,223
Investments held-to-maturity	0	2,100
Investment in subsidiary	513,083	511,841
Loan to subsidiary	30,000	35,000
Other assets	515	352
Total assets	564,824	559,670
Liabilities
Subordinated debentures	30,000	35,000
Accrued expenses and other liabilities	1,252	243
Total liabilities	31,252	35,243
Stockholders Equity
Common stock	23,901	24,296
Additional paid in capital	165,871	175,588
Retained earnings	350,414	325,840
Accumulated other comprehensive income (loss)	(6,614)	(1,297)
Total stockholders equity	533,572	524,427
Total liabilities and stockholders equity	$ 564,824	$ 559,670