Investment Securities - Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Amortized Cost
Due after one year through five years	$ 254,415
Due after five years through ten years	400,929
Total contractual maturities	655,344
Mortgage- and asset-backed securities	4,521,271
Amortized Cost	5,176,615	$ 4,068,766
Fair Value
Due after one year through five years	247,083
Due after five years through ten years	388,057
Total contractual maturities	635,140
Mortgage- and asset-backed securities	4,442,374
Total securities available for sale	5,077,514	4,027,265
Government agency mortgage-backed securities
Amortized Cost
Mortgage- and asset-backed securities	190,485
Amortized Cost	190,485	56,490
Fair Value
Mortgage- and asset-backed securities	185,663
Total securities available for sale	185,663	55,982
Government-sponsored enterprises mortgage-backed securities
Amortized Cost
Mortgage- and asset-backed securities	208,034
Amortized Cost	208,034	10,185
Fair Value
Mortgage- and asset-backed securities	204,385
Total securities available for sale	204,385	10,745
Non-government asset-backed securities
Amortized Cost
Mortgage- and asset-backed securities	12,592
Amortized Cost	12,592	95,453
Fair Value
Mortgage- and asset-backed securities	12,583
Total securities available for sale	12,583	95,310
Collateralized mortgage obligations: Government agency
Amortized Cost
Mortgage- and asset-backed securities	3,409,822
Amortized Cost	3,409,822	2,261,526
Fair Value
Mortgage- and asset-backed securities	3,351,822
Total securities available for sale	3,351,822	2,239,934
Collateralized mortgage obligations: Government-sponsored enterprises
Amortized Cost
Mortgage- and asset-backed securities	700,338
Amortized Cost	700,338	1,046,854
Fair Value
Mortgage- and asset-backed securities	687,921
Total securities available for sale	$ 687,921	$ 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 investment in available-for-sale debt securities with a single maturity date.

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