Parent Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Activities
Net income	$ 95,644	$ 75,516	$ 17,471
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on sale of investments	299	0	(346)
Excess tax deficiencies from stock-based compensation	223	8	0
Net cash provided by operating activities	334,095	183,793	186,843
Investing Activities
Proceeds from sales, maturities and prepayments of investment securities, available-for-sale	1,864,334	2,041,416	1,024,508
Net addition of premises and equipment	(8,977)	(10,730)	(17,492)
Net cash provided by (used in) investment activities	149,237	(579,646)	(529,096)
Financing Activities
Net increase in other borrowed funds	(1,502)	180	(9,867)
Cash dividends paid	(44,232)	(47,472)	(37,395)
Excess tax deficiencies from stock-based compensation	(223)	(8)	0
Proceeds from stock options exercised	4,326	81	0
Net cash used in financing activities	(514,715)	454,861	365,194
Net increase (decrease) in cash and cash equivalents	(31,383)	59,008	22,941
Cash and cash equivalents at beginning of period	187,040	128,032	105,091
Cash and cash equivalents at end of period	155,657	187,040	128,032
Parent Company
Operating Activities
Net income	95,644	75,516	17,091
Adjustments to reconcile net income to net cash provided by operating activities:
Subsidiary income (in excess of) less than dividends distributed	(37,129)	(1,040)	22,825
Loss on sale of investments	3,248	0	0
Excess tax deficiencies from stock-based compensation	223	8	0
Net change in other assets and other liabilities	2,575	3,684	1,215
Net cash provided by operating activities	64,561	78,168	41,131
Investing Activities
Proceeds from sales, maturities and prepayments of investment securities, available-for-sale	26,561	787	1,376
Changes in investment securities and other stock - intercompany	(946)	(19,183)	0
Equity contribution to subsidiaries	(11,336)	(28,500)	(1,110)
Net addition of premises and equipment	(603)	(2,927)	(1,920)
Net cash provided by (used in) investment activities	13,676	(49,823)	(1,654)
Financing Activities
Net increase in other borrowed funds	144	143	143
Cash dividends paid	(44,232)	(47,472)	(37,395)
Excess tax deficiencies from stock-based compensation	(223)	(8)	0
Proceeds from stock options exercised	4,326	81	0
Net cash used in financing activities	(39,985)	(47,256)	(37,252)
Net increase (decrease) in cash and cash equivalents	38,252	(18,911)	2,225
Cash and cash equivalents at beginning of period	12,427	31,338	29,113
Cash and cash equivalents at end of period	$ 50,679	$ 12,427	$ 31,338