Investment Securities - Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Amortized Cost
Due in one year or less	$ 21,141
Due after one year through five years	50,000
Due after five years through ten years	88,000
Total contractual maturities	159,141
Mortgage- and asset-backed securities	4,406,840
Amortized Cost	4,565,981	$ 4,068,766
Fair Value
Due in one year or less	21,150
Due after one year through five years	50,067
Due after five years through ten years	88,191
Total contractual maturities	159,408
Mortgage- and asset-backed securities	4,441,859
Total securities available for sale	4,601,267	4,027,265
Government agency mortgage-backed securities
Amortized Cost
Mortgage- and asset-backed securities	191,016
Amortized Cost	191,016	56,490
Fair Value
Mortgage- and asset-backed securities	192,178
Total securities available for sale	192,178	55,982
Government-sponsored enterprises mortgage-backed securities
Amortized Cost
Mortgage- and asset-backed securities	8,993
Amortized Cost	8,993	10,185
Fair Value
Mortgage- and asset-backed securities	9,515
Total securities available for sale	9,515	10,745
Non-government asset-backed securities
Amortized Cost
Mortgage- and asset-backed securities	36,105
Amortized Cost	36,105	95,453
Fair Value
Mortgage- and asset-backed securities	36,089
Total securities available for sale	36,089	95,310
Collateralized mortgage obligations: Government agency
Amortized Cost
Mortgage- and asset-backed securities	3,104,344
Amortized Cost	3,104,344	2,261,526
Fair Value
Mortgage- and asset-backed securities	3,134,301
Total securities available for sale	3,134,301	2,239,934
Collateralized mortgage obligations: Government-sponsored enterprises
Amortized Cost
Mortgage- and asset-backed securities	1,066,382
Amortized Cost	1,066,382	1,046,854
Fair Value
Mortgage- and asset-backed securities	1,069,776
Total securities available for sale	$ 1,069,776	$ 1,029,337

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the next rolling twelve months following the latest balance sheet. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments and fair value hedge accounting adjustments. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth through tenth rolling twelve months following the latest balance sheet. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the sixth through tenth rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second through fifth rolling twelve months following the latest balance sheet. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the second through fifth rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of investment in available-for-sale debt securities with a single maturity date.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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