Investment Securities Investments in Any One Issuer Exceeding Ten Percent of Equity (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	$ 1,018,774	$ 1,161,633
Available-for-sale, fair value	994,065	$ 1,149,534
Credit Concentration Risk
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	719,388
Available-for-sale, fair value	$ 695,064
Stockholders' Equity, Total
Concentration Risk [Line Items]
Concentration risk percentage	10.00%
Government National Mortgage Association \| Credit Concentration Risk
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	$ 81,247
Available-for-sale, fair value	78,482
Federal Home Loan Mortgage Corporation \| Credit Concentration Risk
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	321,097
Available-for-sale, fair value	308,914
Federal Home Loan Bank \| Credit Concentration Risk
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	109,761
Available-for-sale, fair value	107,661
Federal National Mortgage Association \| Credit Concentration Risk
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	207,283
Available-for-sale, fair value	$ 200,007

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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