Fair Value Measurements (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Fair Value Measurements
Aggregate fair value of PrimeLending's mortgage loans held for sale accounted for under the Fair Value Option	$ 1,050,000,000	$ 1,400,000,000
Unpaid principal balance of PrimeLending loans held for sale accounted under the fair value option	1,000,000,000	1,360,000,000
Financial assets and liabilities
Trading securities	43,254,000	90,113,000
Available for sale securities	1,279,381,000	990,953,000
Level 2
Financial assets and liabilities
Time deposits	6,936,527,000	4,698,848,000
Total Fair Value
Financial assets and liabilities
Time deposits	6,936,527,000	4,698,848,000
Recurring | Level 1
Financial assets and liabilities
Cash and cash equivalents	1,016,274,000	726,460,000
Available for sale securities	20,996,000	20,428,000
Recurring | Level 2
Financial assets and liabilities
Trading securities	43,254,000	90,113,000
Available for sale securities	1,198,783,000	914,248,000
Loans held for sale	1,046,152,000	1,400,737,000
Derivative assets	32,967,000	15,697,000
Time deposits		1,073,000
Trading liabilities	46,000	3,164,000
Derivative liabilities	28,375,000	1,080,000
Recurring | Level 3
Financial assets and liabilities
Available for sale securities	59,602,000	56,277,000
Mortgage servicing asset	13,401,000	2,080,000
Recurring | Total Fair Value
Financial assets and liabilities
Cash and cash equivalents	1,016,274,000	726,460,000
Trading securities	43,254,000	90,113,000
Available for sale securities	1,279,381,000	990,953,000
Loans held for sale	1,046,152,000	1,400,737,000
Derivative assets	32,967,000	15,697,000
Mortgage servicing asset	13,401,000	2,080,000
Time deposits		1,073,000
Trading liabilities	46,000	3,164,000
Derivative liabilities	$ 28,375,000	$ 1,080,000