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]
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]
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]
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]
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