Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Held to maturity:
Amortized Cost	$ 525,708	$ 572,922
Gross Unrealized Gains	12,061	18,078
Gross Unrealized Losses	(7,633)	(4,290)
Estimated Fair Value	530,136	586,710
U.S. government-sponsored mortgage-backed securities
Held to maturity:
Amortized Cost	524,840	572,232
Gross Unrealized Gains	12,061	18,078
Gross Unrealized Losses	(7,633)	(4,290)
Estimated Fair Value	529,268	586,020
Trust preferred securities
Held to maturity:
Amortized Cost	868	690
Estimated Fair Value	$ 868	$ 690

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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