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, 2018	$ 1,478,595		$ 1,337,436	$ 134,055	$ 7,104
Balance, beginning of the period (in shares) at Dec. 31, 2018		35,182,772
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	33,346			33,346
Other comprehensive income, net of income tax	12,790				12,790
Accrual of dividends on common stock	(14,490)			(14,490)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	950		950
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		(30,026)
Balance, end of the period at Mar. 31, 2019	$ 1,511,191		1,338,386	152,911	19,894
Balance, end of the period (in shares) at Mar. 31, 2019		35,152,746
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 0.41
Balance, beginning of the period at Dec. 31, 2018	$ 1,478,595		1,337,436	134,055	7,104
Balance, beginning of the period (in shares) at Dec. 31, 2018		35,182,772
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	112,623
Balance, end of the period at Sep. 30, 2019	$ 1,530,935		1,286,711	203,704	40,520
Balance, end of the period (in shares) at Sep. 30, 2019		34,173,357
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 1.23
Balance, beginning of the period at Mar. 31, 2019	$ 1,511,191		1,338,386	152,911	19,894
Balance, beginning of the period (in shares) at Mar. 31, 2019		35,152,746
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	39,700			39,700
Other comprehensive income, net of income tax	16,016				16,016
Repurchase of common stock	(32,073)		(32,073)
Repurchase of common stock (in shares)		(600,000)
Accrual of dividends on common stock	(14,354)			(14,354)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	575		575
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		20,897
Balance, end of the period at Jun. 30, 2019	$ 1,521,055		1,306,888	178,257	35,910
Balance, end of the period (in shares) at Jun. 30, 2019		34,573,643
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 0.41
Net income	$ 39,577			39,577
Other comprehensive income, net of income tax	4,610				4,610
Repurchase of common stock	(21,849)		(21,849)
Repurchase of common stock (in shares)		(400,000)
Accrual of dividends on common stock	(14,130)			(14,130)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	1,672		1,672
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		(286)
Balance, end of the period at Sep. 30, 2019	$ 1,530,935		1,286,711	203,704	40,520
Balance, end of the period (in shares) at Sep. 30, 2019		34,173,357
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 0.41
Net income	$ 33,655			33,655
Other comprehensive income, net of income tax	(7,264)				(7,264)
Accrual of dividends on common stock	(50,521)			(50,521)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	2,029		2,029
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		(132)
Business acquisition	85,200		85,200
Business acquisition (in shares)		1,578,351
Balance, end of the period at Dec. 31, 2019	$ 1,594,034		1,373,940	186,838	33,256
Balance, end of the period (in shares) at Dec. 31, 2019		35,751,576
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative dividends declared per common share	$ 1.41
New credit standard (Topic 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
Repurchase of common stock	(31,775)		(31,775)
Repurchase of common stock (in shares)		(624,780)
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)
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