CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comp. Income (Loss), net
Common Stock, Dividends, Per Share, Cash Paid	$ 0.16
Balance at Dec. 31, 2018	$ 3,965,940	$ 77,484	$ 3,107,431	$ 833,130	$ (52,105)
Balance (in shares) at Dec. 31, 2018		77,484,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee common stock options and related tax benefits	130	$ 5	125
Exercise of employee common stock options and related tax benefits (in shares)		5,000
Common dividends paid	(12,545)			(12,545)
Repurchase of common stock	(30,049)	$ (543)	(29,506)
Repurchase of common stock (in shares)		(543,000)
Issuance of restricted common shares, net of forfeitures	0	$ 180	(180)
Issuance of restricted common shares, net of forfeitures (in shares)		180,000
Restricted shares withheld for taxes & related tax benefit	(3,487)	$ (62)	(3,425)
Restricted shares withheld for taxes (in shares)		(62,000)
Stock-based compensation expense	4,913		4,913
Net income	93,960			93,960
Other comprehensive income (loss)	37,077				37,077
Balance at Mar. 31, 2019	$ 4,055,939	$ 77,064	3,079,358	914,545	(15,028)
Balance (in shares) at Mar. 31, 2019		77,064,000
Common Stock, Dividends, Per Share, Cash Paid	$ 0.16
Balance at Dec. 31, 2019	$ 4,355,748	$ 76,564	3,064,467	1,184,183	30,534
Balance (in shares) at Dec. 31, 2019		76,564,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee common stock options and related tax benefits	5	$ 1	4
Exercise of employee common stock options and related tax benefits (in shares)		1,000
Common dividends paid	(12,442)			(12,442)
Repurchase of common stock	(50,790)	$ (1,015)	(49,775)
Repurchase of common stock (in shares)		(1,015,000)
Issuance of restricted common shares, net of forfeitures	0	$ 198	(198)
Issuance of restricted common shares, net of forfeitures (in shares)		198,000
Issuance of common stock pursuant to performance-based vesting restricted stock units, net of shares withheld for taxes and related tax benefit	2,468	$ 84	(2,552)
Issuance of common stock pursuant to restricted stock unit agreement, net of shares withheld for taxes and related tax benefit (in shares)		84,000
Restricted shares withheld for taxes & related tax benefit	(1,958)	$ (32)	(1,926)
Restricted shares withheld for taxes (in shares)		(32,000)
Stock-based compensation expense	5,501		5,501
Net income	28,356			28,356
Other comprehensive income (loss)	94,972				94,972
Balance at Mar. 31, 2020	4,385,128	$ 75,800	$ 3,015,521	1,168,301	$ 125,506
Balance (in shares) at Mar. 31, 2020		75,800,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ (31,796)			$ (31,796)