Selected Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 123,995	$ 126,718	$ 111,950	$ 101,075	$ 103,303	$ 110,045	$ 107,639	$ 96,964	$ 463,739	$ 417,951	$ 372,850
Interest expense	46,402	50,983	47,271	41,771	41,779	46,044	40,317	31,933	186,429	160,074	105,507
Net interest income	77,593	75,735	64,679	59,304	61,524	64,001	67,322	65,031	277,310	257,877	267,343
Provision for loan and lease losses	9,689	4,426	5,346	4,767	1,385	2,924	(784)	2,117	24,227	5,642	6,768
Non-interest income	25,813	23,369	12,036	19,718	19,877	2,084	16,127	20,910	80,938	58,998	78,910
Non-interest expenses	58,740	59,592	59,582	53,984	57,045	57,104	53,750	52,280	231,901	220,179	215,606
Income before income tax expense	34,977	35,086	11,787	20,271	22,971	6,057	30,483	31,544	102,120	91,054	123,879
Provision for income taxes	7,451	8,020	2,491	4,831	5,109	28	6,820	7,402	22,793	19,359	45,042
Net income	27,526	27,066	9,296	15,440	17,862	6,029	23,663	24,142	79,327	71,695	78,837
Preferred stock dividends	3,615	3,615	3,615	3,615	3,615	3,615	3,615	3,615	14,459	14,459	14,459
Net income available to common shareholders	$ 23,911	$ 23,451	$ 5,681	$ 11,825	$ 14,247	$ 2,414	$ 20,048	$ 20,527	$ 64,868	$ 57,236	$ 64,378
Earnings per common share:
Basic earnings per share (usd per share)	$ 0.76	$ 0.75	$ 0.18	$ 0.38	$ 0.45	$ 0.08	$ 0.64	$ 0.65	$ 2.08	$ 1.81	$ 2.10
Diluted earnings per share (usd per share)	$ 0.75	$ 0.74	$ 0.18	$ 0.38	$ 0.44	$ 0.07	$ 0.62	$ 0.64	$ 2.05	$ 1.78	$ 1.97
Loss upon acquisition of interest-only GNMA securities			$ 7,500						$ 7,476	$ 0	$ 0
Loss on sale of investment securities						$ (18,700)			$ 1,001	$ (18,659)	$ 8,800