Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investment securities available for sale:
Investment securities available for sale	$ 3,687,470	$ 4,680,226
Trading assets	48,576	52,398
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	47,143	51,103
Fair Value, Inputs, Level 1
Investment securities available for sale:
Investment securities available for sale	2,636	2,602
Fair Value, Inputs, Level 2
Investment securities available for sale:
Investment securities available for sale	3,684,834	4,677,424
Trading assets	50,107	54,974
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	48,674	53,679
Fair Value, Inputs, Level 3
Investment securities available for sale:
Investment securities available for sale	0	200
Trading assets	2,839	3,114
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | US Treasury Securities
Investment securities available for sale:
Investment securities available for sale	1,002	1,000
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Other Debt And Other Equity Securities
Investment securities available for sale:
Investment securities available for sale	1,634	1,602
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Total investment securities available for sale
Investment securities available for sale:
Investment securities available for sale	2,636	2,602
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | FNMA / FHLMC
Investment securities available for sale:
Investment securities available for sale	546,525	639,930
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | GNMA
Investment securities available for sale:
Investment securities available for sale	1,714,178	2,004,475
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Private Label
Investment securities available for sale:
Investment securities available for sale	1,086	1,121
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | GNMA Commercial Mortgage-Related Securities
Investment securities available for sale:
Investment securities available for sale	1,419,872	2,028,898
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Debt And Other Equity Securities
Investment securities available for sale:
Investment securities available for sale	3,173	3,000
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Total investment securities available for sale
Investment securities available for sale:
Investment securities available for sale	3,684,834	4,677,424
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Residential Loans Held For Sale Member
Investment securities available for sale:
Trading assets	41,620	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Interest rate-related instruments — customer and mirror
Investment securities available for sale:
Trading assets	28,105	33,671
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	27,691	33,188
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Foreign currency exchange forwards
Investment securities available for sale:
Trading assets	1,480	2,002
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	1,412	1,943
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commodity contracts
Investment securities available for sale:
Trading assets	18,991	16,725
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	18,040	15,972
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Purchased options (time deposit)
Investment securities available for sale:
Trading assets	1,531	2,576
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	1,531	2,576
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Debt And Other Equity Securities
Investment securities available for sale:
Investment securities available for sale	0	200
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Total investment securities available for sale
Investment securities available for sale:
Investment securities available for sale	0	200
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Interest rate lock commitments (mortgage)
Investment securities available for sale:
Trading assets	2,680	206
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Forward commitments (mortgage)
Investment securities available for sale:
Trading assets	$ 159	$ 2,908