Fair Value Measurement and Fair Value of Financial Instruments (Details 7) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Financial assets:
Cash and cash equivalents	$ 1,736,749	$ 1,878,503	$ 1,666,832	$ 1,360,887
Interest-bearing deposits with banks	404,946	323,148
Resale agreements	1,250,000	2,000,000
Restricted equity securities	73,322	72,775
Loans held-for-sale	178	23,076
Loans held-for-investment, net	28,239,431	25,242,619
Held-to-maturity investment security	0	143,971
Customer deposits:
Short-term borrowings	24,813	60,050
FHLB advances	323,323	321,643
Repurchase agreements	50,000	350,000
Long-term debt	176,513	186,327
Carrying amount of repurchase agreements eligible for netting against resale agreements	400,000	100,000
Gross repurchase agreements	450,000	450,000
Carrying Amount
Financial assets:
Cash and cash equivalents	1,736,749	1,878,503
Interest-bearing deposits with banks	404,946	323,148
Resale agreements	1,250,000	2,000,000
Restricted equity securities	73,322	72,775
Loans held-for-sale	178	23,076
Loans held-for-investment, net	28,239,431	25,242,619
Accrued interest receivable	111,710	100,524
Held-to-maturity investment security		143,971
Customer deposits:
Demand, checking, savings and money market deposits	25,517,121	24,275,714
Time deposits	5,794,541	5,615,269
Short-term borrowings	24,813	60,050
FHLB advances	323,323	321,643
Repurchase agreements	50,000	350,000
Long-term debt	176,513	186,327
Accrued interest payable	11,017	9,440
Estimated Fair Value
Financial assets:
Cash and cash equivalents	1,736,749	1,878,503
Interest-bearing deposits with banks	404,946	323,148
Resale agreements	1,236,413	1,980,457
Restricted equity securities	73,322	72,775
Loans held-for-sale	178	23,076
Loans held-for-investment, net	27,635,961	24,915,143
Accrued interest receivable	111,710	100,524
Held-to-maturity investment security		144,593
Customer deposits:
Demand, checking, savings and money market deposits	25,517,121	24,275,714
Time deposits	5,787,188	5,611,746
Short-term borrowings	24,813	60,050
FHLB advances	336,741	334,859
Repurchase agreements	105,269	411,368
Long-term debt	139,649	186,670
Accrued interest payable	11,017	9,440
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	1,736,749	1,878,503
Interest-bearing deposits with banks	0	0
Resale agreements	0	0
Restricted equity securities	0	0
Loans held-for-sale	0	0
Loans held-for-investment, net	0	0
Accrued interest receivable	0	0
Held-to-maturity investment security		0
Customer deposits:
Demand, checking, savings and money market deposits	0	0
Time deposits	0	0
Short-term borrowings	0	0
FHLB advances	0	0
Repurchase agreements	0	0
Long-term debt	0	0
Accrued interest payable	0	0
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Cash and cash equivalents	0	0
Interest-bearing deposits with banks	404,946	323,148
Resale agreements	1,236,413	1,980,457
Restricted equity securities	73,322	72,775
Loans held-for-sale	178	23,076
Loans held-for-investment, net	0	0
Accrued interest receivable	111,710	100,524
Held-to-maturity investment security		0
Customer deposits:
Demand, checking, savings and money market deposits	25,517,121	24,275,714
Time deposits	5,787,188	5,611,746
Short-term borrowings	24,813	60,050
FHLB advances	336,741	334,859
Repurchase agreements	105,269	411,368
Long-term debt	139,649	186,670
Accrued interest payable	11,017	9,440
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and cash equivalents	0	0
Interest-bearing deposits with banks	0	0
Resale agreements	0	0
Restricted equity securities	0	0
Loans held-for-sale	0	0
Loans held-for-investment, net	27,635,961	24,915,143
Accrued interest receivable	0	0
Held-to-maturity investment security		144,593
Customer deposits:
Demand, checking, savings and money market deposits	0	0
Time deposits	0	0
Short-term borrowings	0	0
FHLB advances	0	0
Repurchase agreements	0	0
Long-term debt	0	0
Accrued interest payable	$ 0	$ 0