Investment Securities - Schedule of Contractual Maturities of Securities Available-for-Sale (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Investments Debt And Equity Securities [Abstract]
Available-for-Sale, Due in one year or less, Amortized Cost	$ 1,222
Available-for-Sale, Due after one year through five years, Amortized Cost	1,157
Available-for-Sale, Due after five years through ten years, Amortized Cost	61,915
Available-for-Sale, Due after ten years, Amortized Cost	217,243
Available-for-Sale, Mortgage-backed securities, Amortized Cost	2,094,100
Available-for-Sale, Total, Amortized Cost	2,375,637
Available-for-Sale, Due in one year or less, Estimated Fair Value	1,226
Available-for-Sale, Due after one year through five years, Estimated Fair Value	1,148
Available-for-Sale, Due after five years through ten years, Estimated Fair Value	61,672
Available-for-Sale, Due after ten years, Estimated Fair Value	226,304
Available-for-Sale, Mortgage-backed securities, Estimated Fair Value	2,171,294
Available-for-Sale, Total, Estimated Fair Value	$ 2,461,644

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
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