Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	$ 4,846,088	$ 4,967,414
Trading assets	60,780	32,192
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	62,301	33,430
Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	2,630	2,566
Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	4,843,258	4,964,648
Trading assets	63,235	34,907
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	64,756	36,145
Fair Value, Inputs, Level 3
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	200	200
Trading assets	3,726	1,361
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	1,868	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 | U.S. Treasury securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	1,001	997
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 | Other securities (debt and equity)
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	1,629	1,569
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 | Total investment securities available for sale
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	2,630	2,566
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | FNMA / FHLMC
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	912,860	1,414,626
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | GNMA
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	1,811,529	1,590,003
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Private-label
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	1,200	1,709
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | GNMA commercial mortgage-related securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	2,114,669	1,955,310
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Other securities (debt and equity)
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	3,000	3,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Total investment securities available for sale
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	4,843,258	4,964,648
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Interest rate-related instruments
Assets, Fair Value Disclosure [Abstract]
Trading assets	47,504	29,391
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	49,887	30,886
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Foreign currency exchange forwards
Assets, Fair Value Disclosure [Abstract]
Trading assets	1,063	1,532
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	1,014	1,398
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading assets	12,213	1,269
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	11,400	1,146
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Purchased options (time deposit)
Assets, Fair Value Disclosure [Abstract]
Trading assets	2,455	2,715
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	2,455	2,715
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Other securities (debt and equity)
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	200	200
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Total investment securities available for sale
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	200	200
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Interest rate lock commitments to originate residential mortgage loans held for sale
Assets, Fair Value Disclosure [Abstract]
Trading assets	3,726	958
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Forward commitments to sell residential mortgage loans
Assets, Fair Value Disclosure [Abstract]
Trading assets	0	403
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	$ 1,868	$ 0