Fair Value Measurement and Fair Value of Financial Instruments (Details 5) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Financial assets:
Cash and cash equivalents	$ 2,434,643	$ 1,878,503	$ 2,265,297	$ 1,360,887
Interest-bearing deposits with banks	249,849	323,148
Resale agreements	1,650,000	2,000,000
Held-to-maturity investment security	132,497	143,971
Loans held-for-sale	28,931	23,076
Loans held-for-investment, net	26,198,198	25,242,619
Restricted equity securities	73,019	72,775
Customer deposits:
Short-term borrowings	42,023	60,050
FHLB advances	322,196	321,643
Repurchase agreements	200,000	350,000
Long-term debt	181,388	186,327
Carrying amount of repurchase agreements eligible for netting against resale agreements	250,000	100,000
Gross repurchase agreements	450,000	450,000
Carrying Amount
Financial assets:
Cash and cash equivalents	2,434,643	1,878,503
Interest-bearing deposits with banks	249,849	323,148
Resale agreements	1,650,000	2,000,000
Held-to-maturity investment security	132,497	143,971
Loans held-for-sale	28,931	23,076
Loans held-for-investment, net	26,198,198	25,242,619
Restricted equity securities	73,019	72,775
Accrued interest receivable	102,067	100,524
Customer deposits:
Demand, interest checking, savings and money market deposits	24,700,811	24,275,714
Time deposits	5,842,164	5,615,269
Short-term borrowings	42,023	60,050
FHLB advances	322,196	321,643
Repurchase agreements	200,000	350,000
Long-term debt	181,388	186,327
Accrued interest payable	9,626	9,440
Estimated Fair Value
Financial assets:
Cash and cash equivalents	2,434,643	1,878,503
Interest-bearing deposits with banks	249,849	323,148
Resale agreements	1,628,839	1,980,457
Held-to-maturity investment security	133,656	144,593
Loans held-for-sale	28,931	23,076
Loans held-for-investment, net	25,825,039	24,915,143
Restricted equity securities	73,019	72,775
Accrued interest receivable	102,067	100,524
Customer deposits:
Demand, interest checking, savings and money market deposits	24,700,811	24,275,714
Time deposits	5,837,924	5,611,746
Short-term borrowings	42,023	60,050
FHLB advances	336,619	334,859
Repurchase agreements	260,545	411,368
Long-term debt	182,502	186,670
Accrued interest payable	9,626	9,440
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	2,434,643	1,878,503
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Interest-bearing deposits with banks	249,849	323,148
Resale agreements	1,628,839	1,980,457
Loans held-for-sale	28,931	23,076
Restricted equity securities	73,019	72,775
Accrued interest receivable	102,067	100,524
Customer deposits:
Demand, interest checking, savings and money market deposits	24,700,811	24,275,714
Time deposits	5,837,924	5,611,746
Short-term borrowings	42,023	60,050
FHLB advances	336,619	334,859
Repurchase agreements	260,545	411,368
Long-term debt	182,502	186,670
Accrued interest payable	9,626	9,440
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Held-to-maturity investment security	133,656	144,593
Loans held-for-investment, net	$ 25,825,039	$ 24,915,143