CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Common Stock and Paid in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, beginning of the period at Dec. 31, 2019	$ 1,594,034		$ 1,373,940	$ 186,838	$ 33,256
Balance, beginning of the period (in shares) at Dec. 31, 2019		35,751,576
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New credit standard (ASC 326) - impact in year of adoption	11,215			11,215
Net income	16,882			16,882
Other comprehensive income, net of income tax	46,823				46,823
Accrual of dividends on common stock	(14,583)			(14,583)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	1,534		1,534
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		(24,337)
Repurchase of common stock	(31,775)		(31,775)
Repurchase of common stock (in shares)		(624,780)
Balance, end of the period at Mar. 31, 2020	$ 1,601,700		1,343,699	177,922	80,079
Balance, end of the period (in shares) at Mar. 31, 2020		35,102,459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 0.41
Balance, beginning of the period at Dec. 31, 2019	$ 1,594,034		1,373,940	186,838	33,256
Balance, beginning of the period (in shares) at Dec. 31, 2019		35,751,576
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	76,971
Balance, end of the period at Sep. 30, 2020	$ 1,646,529		1,347,612	222,959	75,958
Balance, end of the period (in shares) at Sep. 30, 2020		35,158,568
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 0.82
Balance, beginning of the period at Mar. 31, 2020	$ 1,601,700		1,343,699	177,922	80,079
Balance, beginning of the period (in shares) at Mar. 31, 2020		35,102,459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,541			23,541
Other comprehensive income, net of income tax	(1,520)				(1,520)
Accrual of dividends on common stock	(15)			(15)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	1,397		1,397
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		55,440
Balance, end of the period at Jun. 30, 2020	1,625,103		1,345,096	201,448	78,559
Balance, end of the period (in shares) at Jun. 30, 2020		35,157,899
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36,548			36,548
Other comprehensive income, net of income tax	(2,601)				(2,601)
Accrual of dividends on common stock	(15,037)			(15,037)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	2,516		2,516
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		669
Balance, end of the period at Sep. 30, 2020	$ 1,646,529		1,347,612	222,959	75,958
Balance, end of the period (in shares) at Sep. 30, 2020		35,158,568
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 0.41
Net income	$ 38,957			38,957
Other comprehensive income, net of income tax	(6,889)				(6,889)
Accrual of dividends on common stock	(14,600)			(14,600)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	2,267		2,267
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		632
Balance, end of the period at Dec. 31, 2020	$ 1,666,264		1,349,879	247,316	69,069
Balance, end of the period (in shares) at Dec. 31, 2020		35,159,200
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 0.41
Net income	$ 46,855			46,855
Other comprehensive income, net of income tax	(56,103)				(56,103)
Accrual of dividends on common stock	(14,589)			(14,589)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	1,714		1,714
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		76,143
Repurchase of common stock	(25,324)		(25,324)
Repurchase of common stock (in shares)		(500,000)
Balance, end of the period at Mar. 31, 2021	$ 1,618,817		1,326,269	279,582	12,966
Balance, end of the period (in shares) at Mar. 31, 2021		34,735,343
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 0.41
Balance, beginning of the period at Dec. 31, 2020	$ 1,666,264		1,349,879	247,316	69,069
Balance, beginning of the period (in shares) at Dec. 31, 2020		35,159,200
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	151,121
Balance, end of the period at Sep. 30, 2021	$ 1,667,119		1,297,145	355,035	14,939
Balance, end of the period (in shares) at Sep. 30, 2021		34,251,991
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 1.23
Balance, beginning of the period at Mar. 31, 2021	$ 1,618,817		1,326,269	279,582	12,966
Balance, beginning of the period (in shares) at Mar. 31, 2021		34,735,343
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	54,382			54,382
Other comprehensive income, net of income tax	25,285				25,285
Accrual of dividends on common stock	(14,459)			(14,459)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	(259)		(259)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		65,545
Repurchase of common stock	(14,555)		(14,555)
Repurchase of common stock (in shares)		(250,000)
Balance, end of the period at Jun. 30, 2021	$ 1,669,211		1,311,455	319,505	38,251
Balance, end of the period (in shares) at Jun. 30, 2021		34,550,888
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 0.41
Net income	$ 49,884			49,884
Other comprehensive income, net of income tax	(23,312)				(23,312)
Accrual of dividends on common stock	(14,354)			(14,354)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	2,339		2,339
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		1,103
Repurchase of common stock	(16,649)		(16,649)
Repurchase of common stock (in shares)		(300,000)
Balance, end of the period at Sep. 30, 2021	$ 1,667,119		$ 1,297,145	$ 355,035	$ 14,939
Balance, end of the period (in shares) at Sep. 30, 2021		34,251,991
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 0.41