Securities - Available-for-Sale Securities Held by Company (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,363,902	$ 1,408,996
Gross Unrealized Gains	898
Gross Unrealized Losses	32,142
Available-for-sale securities, at fair value	1,332,658	1,391,862
Amortized Cost		1,409,996
Gross Unrealized Gains		2,263
Gross Unrealized Losses		19,484
Fair Value		1,392,775
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	289
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Available-for-sale securities, at fair value	289
Obligations of U.S. Government sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	493,371
Gross Unrealized Gains	80
Gross Unrealized Losses	7,553
Available-for-sale securities, at fair value	485,898
Amortized Cost		507,248
Gross Unrealized Gains		278
Gross Unrealized Losses		3,333
Fair Value		504,193
Obligations of U.S. states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	86,260
Gross Unrealized Gains	113
Gross Unrealized Losses	933
Available-for-sale securities, at fair value	85,440
Amortized Cost		91,659
Gross Unrealized Gains		281
Gross Unrealized Losses		421
Fair Value		91,519
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	131,831
Gross Unrealized Gains	168
Gross Unrealized Losses	3,732
Available-for-sale securities, at fair value	128,267
Amortized Cost		139,747
Gross Unrealized Gains		659
Gross Unrealized Losses		2,671
Fair Value		137,735
U.S. Government sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	649,620
Gross Unrealized Gains	537
Gross Unrealized Losses	19,599
Available-for-sale securities, at fair value	630,558
Amortized Cost		667,767
Gross Unrealized Gains		1,045
Gross Unrealized Losses		12,634
Fair Value		656,178
Non-U.S. Government agencies or sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	31
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Available-for-sale securities, at fair value	31
Amortized Cost		75
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		75
U.S. corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,500
Gross Unrealized Gains	0
Gross Unrealized Losses	325
Available-for-sale securities, at fair value	2,175
Amortized Cost		2,500
Gross Unrealized Gains		0
Gross Unrealized Losses		338
Fair Value		2,162
Debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	582,420	601,407
Available-for-sale securities, at fair value	$ 573,802	597,874
Amortized Cost		1,408,996
Gross Unrealized Gains		2,263
Gross Unrealized Losses		19,397
Fair Value		1,391,862
Equity securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		1,000
Gross Unrealized Gains		0
Gross Unrealized Losses		87
Fair Value		$ 913

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Topic 320
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-Section 50
-Paragraph 2
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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