Investment Securities, Securities Available-for-Sale (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Jun. 30, 2021		Dec. 31, 2020	Jun. 30, 2020
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost			$ 350,267		$ 789,175	$ 548,600
Gross unrealized gains			5,249		18,716	20,935
Gross unrealized losses			3,855		159	128
Fair value			351,661		807,732	569,407
U.S. Treasury Notes [Member]
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost			9,905		14,859	64,802
Gross unrealized gains			282		429	583
Gross unrealized losses			0		0	1
Fair value			10,187		15,288	65,384
U.S. Government Agency SBA [Member]
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost			7,323		8,252	9,397
Gross unrealized gains			73		1	1
Gross unrealized losses			49		93	110
Fair value			7,347		8,160	9,288
Mortgage-Backed Securities [Member]
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost	[2]		286,529	[1]	720,562	448,904
Gross unrealized gains	[2]		4,894	[1]	17,359	20,326
Gross unrealized losses	[2]		3,806	[1]	48	5
Fair value	[2]		287,617	[1]	737,873	469,225
Securities Transferred [Abstract]
Fair value of securities transferred to held-to-maturity category		$ 316,900
Corporate Securities [Member]
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost					45,010	10,190
Gross unrealized gains					927	25
Gross unrealized losses					18	12
Fair value					45,919	10,203
Other [Member]
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost			46,510		492	15,307
Gross unrealized gains			0		0	0
Gross unrealized losses			0		0	0
Fair value			$ 46,510		$ 492	$ 15,307

[1] During Q1 2021, the Company transferred $316.9 million of AFS securities to HTM.

[2] All Mortgage-backed securities consist of securities collateralized by residential real estate and were issued by an agency or government-sponsored entity of the U.S. government.