Investment Securities - Securities with gross unrealized losses (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Securities Held to Maturity, Fair Value
Less Than Twelve Months	$ 66,450	$ 456,013	$ 1,062,660
Twelve Months or More	337,108	802,413	341,687
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	324	6,042	24,290
Twelve Months or More	2,611	19,968	14,324
Government-sponsored entities debt
Securities Held to Maturity, Fair Value
Less Than Twelve Months		10,571	39,145
Twelve Months or More	5,742	32,959	8,468
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months		100	1,179
Twelve Months or More	8	652	141
State and municipal obligations
Securities Held to Maturity, Fair Value
Less Than Twelve Months	1,490	40,387	77,373
Twelve Months or More	1,153	14,231	1,348
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months		760	1,617
Twelve Months or More	1	365	32
Mortgage-backed securities
Securities Held to Maturity, Fair Value
Less Than Twelve Months	64,960	405,055	946,142
Twelve Months or More	330,213	755,223	331,871
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	324	5,182	21,494
Twelve Months or More	$ 2,602	$ 18,951	$ 14,151

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- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
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-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922890-210455

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for less than 12 months.

+ References

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for 12 months or longer.

+ References

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