Fair Value (Details 4) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Carrying amount and estimated fair value of financial instruments
Securities available-for-sale	$ 872,675		$ 691,000
Restricted stock	21,050		21,292
FDIC Indemnification Asset	1,171	1,515	2,632	2,384
Accrued interest receivable	11,767		12,024
Deposits	(2,487,028)		(2,276,134)
Level 1
Carrying amount and estimated fair value of financial instruments
Cash and due from banks	20,404		21,333
Federal funds sold	0		0
Securities available-for-sale	662		380
Restricted stock	0		0
Loans, net	0		0
FDIC Indemnification Asset	0		0
Accrued interest receivable	0		0
Deposits	0		0
Short-term borrowings	0		0
Federal Home Loan Bank advances	0		0
Accrued interest payable	0		0
Level 2
Carrying amount and estimated fair value of financial instruments
Cash and due from banks	60,495		65,897
Federal funds sold	3,420		20,800
Securities available-for-sale	859,965		674,587
Restricted stock	0		0
Loans, net			0
FDIC Indemnification Asset	1,171		2,632
Accrued interest receivable	3,475		2,980
Deposits	(2,489,329)		(2,280,910)
Short-term borrowings	(27,929)		(40,551)
Federal Home Loan Bank advances	(60,721)		(124,933)
Accrued interest payable	(770)		(1,163)
Level 3
Carrying amount and estimated fair value of financial instruments
Cash and due from banks	0		0
Federal funds sold	0		0
Securities available-for-sale	12,048		16,033
Restricted stock	0		0
Loans, net	1,845,392		1,916,256
FDIC Indemnification Asset	0		0
Accrued interest receivable	8,292		9,044
Deposits	0		0
Short-term borrowings	0		0
Federal Home Loan Bank advances	0		0
Accrued interest payable	0		0
Carrying Value
Carrying amount and estimated fair value of financial instruments
Cash and due from banks	80,899		87,230
Federal funds sold	3,420		20,800
Securities available-for-sale	872,675		691,000
Restricted stock	21,050		21,292
Loans, net	1,786,601		1,829,978
FDIC Indemnification Asset	1,171		2,632
Accrued interest receivable	11,767		12,024
Deposits	(2,487,028)		(2,276,134)
Short-term borrowings	(27,929)		(40,551)
Federal Home Loan Bank advances	(58,362)		(119,705)
Accrued interest payable	(770)		(1,163)
Fair Value
Carrying amount and estimated fair value of financial instruments
Cash and due from banks	80,899		87,230
Federal funds sold	3,420		20,800
Securities available-for-sale	872,675		691,000
Restricted stock	0		0
Loans, net	1,845,392		1,916,256
FDIC Indemnification Asset	1,171		2,632
Accrued interest receivable	11,767		12,024
Deposits	(2,489,329)		(2,280,910)
Short-term borrowings	(27,929)		(40,551)
Federal Home Loan Bank advances	(60,721)		(124,933)
Accrued interest payable	$ (770)		$ (1,163)