Condensed Financial Information (Parent Company Only) - Condensed Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities:
Net income	$ 86,136	$ 58,224	$ 44,546
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	16,245	17,112	17,368
Write-down of equipment pending disposal	616	70	0
Deferred income tax expense (benefit)	11,276	8,762	2,405
Stock-based compensation expense	2,936	2,485	2,111
Tax benefits from stock-based compensation	1,898	360	204
Excess tax benefits from stock-based compensation	(2,031)	(273)	(124)
Net cash provided by operating activities	150,225	135,822	143,101
Cash flows from investing activities:
Net cash used in investing activities	(204,937)	(141,079)	(125,939)
Cash flows from financing activities:
Redemption of preferred stock	(243)	(40)	(302)
Repayment of junior subordinated debentures held by subsidiary trusts	0	(41,238)	0
Proceeds from issuance of common stock	9,814	1,911	385
Excess tax benefits from stock-based compensation	2,031	273	124
Purchase and retirement of common stock	(448)	(263)	(248)
Dividends paid to common stockholders	(17,909)	(26,208)	(19,233)
Dividends paid to preferred stockholders	0	(3,300)	(3,422)
Net cash used in financing activities	(211,793)	334,142	(230,333)
Net change in cash and cash equivalents	(266,505)	328,885	(213,171)
Cash and cash equivalents at beginning of year	801,332	472,447	685,618
Cash and cash equivalents at end of year	534,827	801,332	472,447
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Transfer of preferred stock pending redemption from equity to liability		50,000
Transfered accrued liabilities to common stock in conjunction with the vesting of liability-classified non-vested stock awards			216
Parent Company
Cash flows from operating activities:
Net income	86,136	58,224	44,546
Adjustments to reconcile net income to cash provided by operating activities:
Undistributed earnings of subsidiaries	(23,748)	(28,914)	(25,444)
Stock-based compensation expense	2,936	2,485	2,111
Tax benefits from stock-based compensation	1,898	360	204
Excess tax benefits from stock-based compensation	(2,031)	(273)	(124)
Other, net	(5,804)	3,327	2,600
Net cash provided by operating activities	59,387	35,209	23,893
Cash flows from investing activities:
Capital expenditures, net of sales	0	1	(3)
Net cash used in investing activities	0	1	(3)
Cash flows from financing activities:
Net (decrease) increase in advances from nonbank subsidiaries	6,992	(2,838)	(2,913)
Redemption of preferred stock	(50,000)	0	0
Repayment of junior subordinated debentures held by subsidiary trusts	0	(41,238)	0
Proceeds from issuance of common stock	9,814	1,911	385
Excess tax benefits from stock-based compensation	2,031	273	124
Purchase and retirement of common stock	(448)	(263)	(248)
Dividends paid to common stockholders	(17,909)	(26,208)	(19,233)
Dividends paid to preferred stockholders	0	(3,300)	(3,422)
Net cash used in financing activities	(49,520)	(71,663)	(25,307)
Net change in cash and cash equivalents	9,867	(36,453)	(1,417)
Cash and cash equivalents at beginning of year	95,407	131,860	133,277
Cash and cash equivalents at end of year	105,274	95,407	131,860
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Transfer of preferred stock pending redemption from equity to liability	$ 50,000