CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Retained Earnings Cumulative-effect adjustment	Retained Earnings	Accumulated other comprehensive Income (loss) Cumulative-effect adjustment	Accumulated other comprehensive Income (loss)	Treasury Stock	Cumulative-effect adjustment	Total
Balance (ASU 2018-02) at Dec. 31, 2017			$ 20,068		$ (20,068)
Balance at Dec. 31, 2017	$ 1,396	$ 2,488,643		$ 139,177		$ (96,383)	$ (282)		$ 2,532,551
Balance (in shares) at Dec. 31, 2017	139,588,782
Increase (Decrease) in Stockholders' Equity
Net income				264,394					264,394
Cash dividends declared				(131,036)					(131,036)
Common stock issued under Employee Stock Purchase Plan		342							342
Common stock issued under Employee Stock Purchase Plan (in shares)	12,341
Equity-based awards	$ 1	6,868		(684)			(53)		6,132
Equity-based awards (in shares)	43,049
Common stock repurchased							(131,800)		(131,800)
Common stock repurchased (in shares)	(4,769,870)
Other comprehensive income (loss), net of tax						(15,744)			(15,744)
Balance at Dec. 31, 2018	$ 1,397	2,495,853		291,919		(132,195)	(132,135)		2,524,839
Balance (in shares) at Dec. 31, 2018	134,874,302
Increase (Decrease) in Stockholders' Equity
Net income				284,392					284,392
Cash dividends declared				(138,246)					(138,246)
Equity-based awards	$ 2	7,824		(993)			(1,764)		5,069
Equity-based awards (in shares)	194,187
Common stock repurchased							(136,242)		(136,242)
Common stock repurchased (in shares)	(5,140,010)
Other comprehensive income (loss), net of tax						100,446			100,446
Balance (ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments) at Dec. 31, 2019			$ (12,517)					$ (12,517)
Balance at Dec. 31, 2019	$ 1,399	2,503,677		437,072		(31,749)	(270,141)		$ 2,640,258
Balance (in shares) at Dec. 31, 2019	129,928,479								129,928,479
Increase (Decrease) in Stockholders' Equity
Net income				185,754					$ 185,754
Cash dividends declared				(135,099)					(135,099)
Common stock issued under Employee Stock Purchase Plan		312							312
Common stock issued under Employee Stock Purchase Plan (in shares)	19,069
Equity-based awards	$ 3	10,025		(1,236)			(1,749)		7,043
Equity-based awards (in shares)	182,483
Common stock repurchased							(5,000)		(5,000)
Common stock repurchased (in shares)	(217,759)
Other comprehensive income (loss), net of tax						63,353			63,353
Balance at Dec. 31, 2020	$ 1,402	$ 2,514,014		$ 473,974		$ 31,604	$ (276,890)		$ 2,744,104
Balance (in shares) at Dec. 31, 2020	129,912,272								129,912,272