Fair Value Measurement and Fair Value of Financial Instruments (Details 5) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Financial assets:
Cash and cash equivalents	$ 2,752,476	$ 1,878,503	$ 1,592,796	$ 1,360,887
Interest-bearing deposits with banks	296,679	323,148
Resale agreements	1,300,000	2,000,000
Held-to-maturity investment security	121,131	143,971
Restricted equity securities	73,173	72,775
Loans held-for-sale	11,649	23,076
Loans held-for-investment, net	26,934,350	25,242,619
Customer deposits:
Short-term borrowings	24,426	60,050
FHLB advances	322,756	321,643
Repurchase agreements	50,000	350,000
Long-term debt	176,450	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	2,752,476	1,878,503
Interest-bearing deposits with banks	296,679	323,148
Resale agreements	1,300,000	2,000,000
Held-to-maturity investment security	121,131	143,971
Restricted equity securities	73,173	72,775
Loans held-for-sale	11,649	23,076
Loans held-for-investment, net	26,934,350	25,242,619
Accrued interest receivable	100,036	100,524
Customer deposits:
Demand, checking, savings and money market deposits	25,080,973	24,275,714
Time deposits	6,073,314	5,615,269
Short-term borrowings	24,426	60,050
FHLB advances	322,756	321,643
Repurchase agreements	50,000	350,000
Long-term debt	176,450	186,327
Accrued interest payable	9,255	9,440
Estimated Fair Value
Financial assets:
Cash and cash equivalents	2,752,476	1,878,503
Interest-bearing deposits with banks	296,679	323,148
Resale agreements	1,279,609	1,980,457
Held-to-maturity investment security	121,803	144,593
Restricted equity securities	73,173	72,775
Loans held-for-sale	11,649	23,076
Loans held-for-investment, net	26,460,495	24,915,143
Accrued interest receivable	100,036	100,524
Customer deposits:
Demand, checking, savings and money market deposits	25,080,973	24,275,714
Time deposits	6,066,948	5,611,746
Short-term borrowings	24,426	60,050
FHLB advances	336,627	334,859
Repurchase agreements	107,564	411,368
Long-term debt	183,589	186,670
Accrued interest payable	9,255	9,440
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	2,752,476	1,878,503
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Interest-bearing deposits with banks	296,679	323,148
Resale agreements	1,279,609	1,980,457
Restricted equity securities	73,173	72,775
Loans held-for-sale	11,649	23,076
Accrued interest receivable	100,036	100,524
Customer deposits:
Demand, checking, savings and money market deposits	25,080,973	24,275,714
Time deposits	6,066,948	5,611,746
Short-term borrowings	24,426	60,050
FHLB advances	336,627	334,859
Repurchase agreements	107,564	411,368
Long-term debt	183,589	186,670
Accrued interest payable	9,255	9,440
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Held-to-maturity investment security	121,803	144,593
Loans held-for-investment, net	$ 26,460,495	$ 24,915,143