Loans (Granite Purchased Loans) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Financing Receivable [Line Items]
Allowance of loan losses	$ 25,085	$ 29,641	$ 29,314	[1]	$ 25,085	$ 38,551	$ 39,795	$ 29,314	$ 38,551	$ 39,360
Loans held for investment	1,189,413		1,177,035	[1]
PI [Member]
Financing Receivable [Line Items]
Loans held for investment	189,159		228,392
PC [Member]
Financing Receivable [Line Items]
Loans held for investment	1,000,254		948,643
Granite Corp [Member]
Financing Receivable [Line Items]
Purchased impaired	189,159		228,392			287,092
Purchased contractual	29,167		34,844
Loans held for investment	218,326		263,236
Unpaid principal balance	220,604		271,060
Granite Corp [Member] | Commercial and agricultural [Member]
Financing Receivable [Line Items]
Purchased impaired	11,964		14,666
Purchased contractual	4,647		7,311
Loans held for investment	16,611		21,977
Unpaid principal balance	15,971		21,692
Granite Corp [Member] | Real estate - construction [Member]
Financing Receivable [Line Items]
Purchased impaired	10,263		2,682
Purchased contractual	0		0
Loans held for investment	10,263		2,682
Unpaid principal balance	10,095		2,677
Granite Corp [Member] | Real estate - mortgage, 1-4 family residential [Member]
Financing Receivable [Line Items]
Purchased impaired	32,813		39,215
Purchased contractual	24,130		27,484
Loans held for investment	56,943		66,699
Unpaid principal balance	58,197		69,200
Granite Corp [Member] | Real estate - mortgage, commercial [Member]
Financing Receivable [Line Items]
Purchased impaired	132,978		170,467
Purchased contractual	390		49
Loans held for investment	133,368		170,516
Unpaid principal balance	135,404		176,347
Granite Corp [Member] | Consumer [Member]
Financing Receivable [Line Items]
Purchased impaired	1,141		1,362
Purchased contractual	0		0
Loans held for investment	1,141		1,362
Unpaid principal balance	937		1,144
Granite Corp [Member] | PI [Member]
Financing Receivable [Line Items]
Allowance of loan losses	4,100		5,400
Granite Corp [Member] | PC [Member]
Financing Receivable [Line Items]
Allowance of loan losses	$ 700		$ 500

[1] Derived from audited consolidated financial statements