Long-Term Debt (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Instruments [Abstract]
Credit facility	$ 0	$ 0
Deferred financing costs	(9,678)	(11,512)
Long-term debt	455,666	394,886
Less current portion	0	0
Long-term debt, less current portion	455,666	394,886
Purchase price of extinguished debt			$ 27,863
Allocated liability component of repurchased debt			9,568
Allocated equity component of repurchased debt			18,295
Loss on early extinguishment of debt	0	8,073	2,030
Interest expense [Abstract]
Contractual coupon interest		12,185	13,998
Non-cash amortization of debt discount	0	13,161	14,146
Other Noncash Interest Expense (Income)		1,623	1,781
Total interest expense related to the debentures		26,969	29,925
Principal amount of repurchased debt		151,546	19,366
Committed and uncommitted short-term credit lines	1,000	6,000
Aggregate annual maturities of long-term debt [Abstract]
Interest paid	14,177	15,450	16,177
Convertible Debt [Member]
Liability and equity components of convertible debentures [Abstract]
Principal amount of the convertible debt		465,644
Unamortized discount		(59,246)
Carrying value of liability component		406,398
Equity component (including temporary equity) - net carrying value		66,248
Revolving Credit Facility [Member]
Line of Credit Facility [Abstract]
Line of credit facility, maximum borrowing capacity	$ 750,000
Line of credit facility, expiration date	Jun. 05, 2024
Incremental revolving commitments	$ 300,000
Basis spread on variable rate	1.50%
Commitment fees	0.25%
Investments pro forma ratio	2.75
Restricted payments pro forma ratio	2.50
Restricted payments, annual limit	$ 100,000
Restricted payments ,total limit	300,000
Restricted payments ,rollover limit	25,000
Restricted payments, unused amount	100,000
Event of default - judgment limit	50,000
Available borrowing capacity	748,931	748,690
Letters of credit outstanding	1,069	1,310
Convertible Senior Notes, Due 2025 [Member]
Debt Instruments [Abstract]
Convertible debt	$ 465,344	406,268
Issuance date	Jun. 12, 2018
Maturity date	Jun. 15, 2025
Cash coupon rate	2.25%
Nonconvertible debt borrowing rate at issuance	5.50%
Effective conversion rate	31.9492
Effective conversion price (in dollars per share)	$ 31.30
130% of the conversion price (in dollars per share)	$ 40.69
Debt instrument percentage of conversion price	130.00%
Debt instrument, percentage of sale price of common stock	98.00%
Maximum threshold of quarterly cash dividends per share of common stock for not adjusting conversion rate of convertible notes (in dollars per share)	$ 0.085
Purchase price of extinguished debt		128,328
Allocated liability component of repurchased debt		118,587
Allocated equity component of repurchased debt		9,741
Loss on early extinguishment of debt		4,600
Liability and equity components of convertible debentures [Abstract]
Principal amount of the convertible debt	$ 465,344	465,344
Unamortized discount		(59,076)
Carrying value of liability component		406,268
Equity component (including temporary equity) - net carrying value		66,127
Interest expense [Abstract]
Contractual coupon interest	10,470	12,097	13,500
Non-cash amortization of debt discount	0	13,118	13,925
Other Noncash Interest Expense (Income)	1,733	1,623	1,816
Total interest expense related to the debentures	12,203	26,838	29,241
Principal amount of repurchased debt		134,656
Net carrying value of repurchased debt		115,978
Convertible Senior Debentures, Due 2040 [Member]
Debt Instruments [Abstract]
Convertible debt	$ 0	130
Interest expense [Abstract]
Principal amount of repurchased debt			1,010
Net carrying value of repurchased debt			417
Convertible Senior Debentures, Due 2041 [Member]
Debt Instruments [Abstract]
Purchase price of extinguished debt		23,355
Allocated liability component of repurchased debt		10,075
Allocated equity component of repurchased debt		13,280
Loss on early extinguishment of debt		3,473
Interest expense [Abstract]
Principal amount of repurchased debt		16,890	16,188
Net carrying value of repurchased debt		6,715	6,282
Convertible Senior Debentures 2042 [Member]
Interest expense [Abstract]
Principal amount of repurchased debt			2,168
Net carrying value of repurchased debt			924
Convertible Senior Debentures [Member]
Interest expense [Abstract]
Contractual coupon interest		88	498
Non-cash amortization of debt discount		43	221
Other Noncash Interest Expense (Income)		0	(35)
Total interest expense related to the debentures		131	$ 684
Convertible Senior Debentures [Member] | Convertible Debt [Member]
Liability and equity components of convertible debentures [Abstract]
Principal amount of the convertible debt		300
Unamortized discount		(170)
Carrying value of liability component		130
Equity component (including temporary equity) - net carrying value		$ 121