Investment Securities - Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Amortized Cost
Due after one year through five years	$ 228,481
Due after five years through ten years	269,704
Total contractual maturities	498,185
Mortgage- and asset-backed securities	4,840,180
Amortized Cost	5,338,365	$ 4,068,766
Fair Value
Due after one year through five years	228,507
Due after five years through ten years	269,875
Total contractual maturities	498,382
Mortgage- and asset-backed securities	4,865,314
Total securities available for sale	5,363,696	4,027,265
Government agency mortgage-backed securities
Amortized Cost
Mortgage- and asset-backed securities	203,685
Amortized Cost	203,685	56,490
Fair Value
Mortgage- and asset-backed securities	204,958
Total securities available for sale	204,958	55,982
Government-sponsored enterprises mortgage-backed securities
Amortized Cost
Mortgage- and asset-backed securities	8,539
Amortized Cost	8,539	10,185
Fair Value
Mortgage- and asset-backed securities	9,000
Total securities available for sale	9,000	10,745
Non-government asset-backed securities
Amortized Cost
Mortgage- and asset-backed securities	19,510
Amortized Cost	19,510	95,453
Fair Value
Mortgage- and asset-backed securities	19,494
Total securities available for sale	19,494	95,310
Collateralized mortgage obligations: Government agency
Amortized Cost
Mortgage- and asset-backed securities	3,522,585
Amortized Cost	3,522,585	2,261,526
Fair Value
Mortgage- and asset-backed securities	3,543,652
Total securities available for sale	3,543,652	2,239,934
Collateralized mortgage obligations: Government-sponsored enterprises
Amortized Cost
Mortgage- and asset-backed securities	1,085,861
Amortized Cost	1,085,861	1,046,854
Fair Value
Mortgage- and asset-backed securities	1,088,210
Total securities available for sale	$ 1,088,210	$ 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 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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Fair value of investment in available-for-sale debt securities with a single maturity date.

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