Investment Securities - Summary of Available-for-Sale Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 761,037	$ 809,725
Gross unrealized gains	2,944	2,288
Gross unrealized losses	(14,444)	(20,911)
Investment securities available-for-sale (at fair value)	749,537	791,102
Residential Mortgage Pass-Through Securities Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	134,173	147,283
Gross unrealized gains	1,269	1,232
Gross unrealized losses	(954)	(1,873)
Investment securities available-for-sale (at fair value)	134,488	146,642
Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	625,776	661,354
Gross unrealized gains	1,675	1,056
Gross unrealized losses	(13,481)	(19,029)
Investment securities available-for-sale (at fair value)	613,970	643,381
Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	619	619
Gross unrealized losses	(9)	(9)
Investment securities available-for-sale (at fair value)	610	610
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	469	469
Investment securities available-for-sale (at fair value)	$ 469	$ 469

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).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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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).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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