PARENT COMPANY STATEMENTS (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended	12 Months Ended
	Jan. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets:
Cash and cash equivalents		$ 138,396	$ 149,647	$ 228,558
Other assets		140,912	152,390
Total assets		7,489,440	7,095,864	7,496,800
Liabilities and shareholders' equity:
Accrued interest and other liabilities		126,150	79,998
Borrowings		102,122	102,097
Shareholders' equity		987,904	875,812	902,778	774,583
Total liabilities and shareholders' equity		7,489,440	7,095,864
Revenues:
Other income		119,020	102,180	99,246
Expenses:
Interest on borrowings		2,477	2,520	2,716
Other expenses		17,310	14,971	16,459
(Loss) Income before tax benefit and equity in undistributed net income of subsidiaries		129,690	111,027	108,805
Income tax benefit		(38,337)	(32,198)	(31,737)
Net income		91,353	78,829	77,068
Comprehensive (loss)/income		148,619	(2,051)	102,237
Operating activities:
Net income		91,353	78,829	77,068
Adjustments to reconcile net income to net cash provided by operating activities
Net change in other assets and other liabilities		10	11,247	292
Net cash provided by operating activities		123,201	103,184	108,424
Investing activities:
Net cash (used in)/provided by investing activities		(332,229)	553,258	(264,260)
Financing activities:
Issuance of common stock	57,500	9,989	15,239	64,145
Purchase of treasury stock		(4,368)	0	0
Sale of treasury stock		959	0	0
Net cash provided by/(used in) financing activities		197,777	(735,353)	59,516
Change in cash and cash equivalents		(11,251)	(78,911)	(96,320)
Cash and cash equivalents at beginning of year	324,878	149,647	228,558	324,878
Cash and cash equivalents at end of year		138,396	149,647	228,558
Supplemental disclosures of cash flow information:
Cash paid for interest		11,937	30,141	51,541
Supplemental disclosures of noncash financing activities
Dividends declared and unpaid		12,254	11,332	10,699
Parent Company [Member]
Assets:
Cash and cash equivalents		106,957	83,783	43,800
Investment securities		3,622	3,601
Investment in and advances to subsidiaries		984,561	895,211
Other assets		9,608	8,847
Total assets		1,104,748	991,442
Liabilities and shareholders' equity:
Accrued interest and other liabilities		14,722	13,533
Borrowings		102,122	102,097
Shareholders' equity		987,904	875,812
Total liabilities and shareholders' equity		1,104,748	991,442
Revenues:
Dividends from subsidiaries		61,100	66,000	0
Interest and dividends on investments		88	91	98
Other income		0	9	198
Total revenues		61,188	66,100	296
Expenses:
Interest on borrowings		2,477	2,520	2,716
Other expenses		37	61	155
Total expenses		2,514	2,581	2,871
(Loss) Income before tax benefit and equity in undistributed net income of subsidiaries		58,674	63,519	(2,575)
Income tax benefit		581	862	1,274
(Loss) Income before equity in undistributed net income of subsidiaries		59,255	64,381	(1,301)
Equity in undistributed net income of subsidiaries		32,098	14,448	78,369
Net income		91,353	78,829	77,068
Comprehensive (loss)/income		148,619	(2,051)	102,237
Operating activities:
Net income		91,353	78,829	77,068
Adjustments to reconcile net income to net cash provided by operating activities
(Gain)/loss on sale of investments		0	(9)	0
Equity in undistributed net income of subsidiaries		(32,098)	(14,448)	(78,369)
Net change in other assets and other liabilities		(479)	(221)	(746)
Net cash provided by operating activities		58,776	64,151	(2,047)
Investing activities:
Purchase of investment securities		0	0	(3)
Proceeds from sale of investment securities		3	114	30
Capital contributions to subsidiaries		0	0	(20,081)
Net cash (used in)/provided by investing activities		3	114	(20,054)
Financing activities:
Issuance of common stock		13,982	19,200	67,813
Purchase of treasury stock		(4,368)	0	0
Sale of treasury stock		959	0	0
Cash dividends paid		(46,178)	(43,482)	(40,765)
Net cash provided by/(used in) financing activities		(35,605)	(24,282)	27,048
Change in cash and cash equivalents		23,174	39,983	4,947
Cash and cash equivalents at beginning of year	38,853	83,783	43,800	38,853
Cash and cash equivalents at end of year		106,957	83,783	43,800
Supplemental disclosures of cash flow information:
Cash paid for interest		2,473	2,521	2,738
Supplemental disclosures of noncash financing activities
Dividends declared and unpaid		$ 12,254	$ 11,332	$ 10,699