Securities - Schedule of Available-for-Sales Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,385,805	$ 1,408,996
Gross Unrealized Gains	640
Gross Unrealized Losses	42,755
Fair Value	1,343,690	1,391,862
Amortized Cost		1,409,996
Gross Unrealized Gains		2,263
Gross Unrealized Losses		19,484
Available-for-sale securities, at fair value		1,392,775
Obligations of U.S. Government sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	498,540
Gross Unrealized Gains	0
Gross Unrealized Losses	10,941
Fair Value	487,599
Amortized Cost		507,248
Gross Unrealized Gains		278
Gross Unrealized Losses		3,333
Available-for-sale securities, at fair value		504,193
Obligations of U.S. states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	87,510
Gross Unrealized Gains	74
Gross Unrealized Losses	1,374
Fair Value	86,210
Amortized Cost		91,659
Gross Unrealized Gains		281
Gross Unrealized Losses		421
Available-for-sale securities, at fair value		91,519
U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	124,343
Gross Unrealized Gains	261
Gross Unrealized Losses	4,728
Fair Value	119,876
Amortized Cost		139,747
Gross Unrealized Gains		659
Gross Unrealized Losses		2,671
Available-for-sale securities, at fair value		137,735
U.S. Government sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	672,859
Gross Unrealized Gains	305
Gross Unrealized Losses	25,387
Fair Value	647,777
Amortized Cost		667,767
Gross Unrealized Gains		1,045
Gross Unrealized Losses		12,634
Available-for-sale securities, at fair value		656,178
Non-U.S. Government agencies or sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	53
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	53
Amortized Cost		75
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Available-for-sale securities, at fair value		75
U.S. corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,500
Gross Unrealized Gains	0
Gross Unrealized Losses	325
Fair Value	2,175
Amortized Cost		2,500
Gross Unrealized Gains		0
Gross Unrealized Losses		338
Available-for-sale securities, at fair value		2,162
Total available-for-sale securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	588,550	601,407
Fair Value	$ 575,984	597,874
Amortized Cost		1,408,996
Gross Unrealized Gains		2,263
Gross Unrealized Losses		19,397
Available-for-sale securities, at fair value		1,391,862
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,000
Gross Unrealized Gains		0
Gross Unrealized Losses		87
Available-for-sale securities, at fair value		$ 913

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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