Debt (Convertible Debt) (Details)		12 Months Ended
	May 12, 2017 USD ($) $ / shares	Dec. 31, 2020 USD ($) Integer shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) shares	Dec. 13, 2019 USD ($)	Sep. 27, 2019 USD ($)	Nov. 13, 2017 USD ($)	May 24, 2017 USD ($)
Debt Instrument
Options issued in debt conversion (in shares) | shares				114,778
Amortization of debt issuance costs		$ 1,746,000	$ 1,996,000	$ 1,806,000
Purchase of call options related to convertible notes	$ 20,500,000
Convertible Debt [Abstract]
Capped call transaction cap price (in dollars per share) | $ / shares	$ 88.7570
Effective interest rate								5.00%
Interest Expense, Debt [Abstract]
Accretion of convertible notes discount		2,860,000	2,760,000	2,596,000
Stock conversion amount				7,600,000
2024 Notes
Debt Instrument
Convertible notes face amount		199,500,000	199,500,000					$ 200,000,000.0
Unamortized discount		10,581,000	13,440,000
Carrying value of liability		188,919,000	186,060,000					179,500,000
Amount before overallotment	$ 175,000,000.0
Debt Instrument face amount overallotment								25,000,000.0
Annual principal interest rate	3.25%
Multiple, Debt Instrument	$ 1,000					$ 1,000
Debt Instrument, Repurchased Face Amount						$ 500,000
Percent, Debt Instrument, Repurchase Amount						0.25%
Equity component		20,408,000	20,408,000					20,500,000
Deferred finance costs, gross								(7,400,000)
Amortization of debt issuance costs		$ 900,000	900,000	800,000
Convertible Debt [Abstract]
Conversion rate	15.3227
Conversion price (in dollars per share) | $ / shares	$ 65.2626
Contingent conversion price (in dollars per shares) | $ / shares	$ 84.8413
Aggregate shares to be issued upon conversion, convertible (in shares) | shares		3,056,879
Convertible debt stock price threshold trigger percent		130.00%
Convertible debt trading days threshold | Integer		20
Convertible, threshold consecutive trading days | Integer		30
Percentage of average of closing price of common stock		98.00%
Debt issuance costs, recorded to APIC								700,000
Debt issuance costs, recorded as contra-debt								$ 6,700,000
Interest Expense, Debt [Abstract]
Contractual coupon rate of interest		$ 6,484,000	6,503,000	6,500,000
Accretion of convertible notes discount		2,860,000	2,753,000	2,596,000
Interest expense		9,344,000	9,256,000	$ 9,096,000
2017 Notes
Debt Instrument
Options issued in debt conversion (in shares) | shares				114,778
Debt Instrument, Repurchased Face Amount	$ 103,500,000						$ 11,500,000
Revolving Credit Facility
Debt Instrument
Amortization of debt issuance costs		700,000	1,000,000.0	$ 1,000,000.0
Credit Agreement 2019 [Member] | Revolving Credit Facility
Interest Expense, Debt [Abstract]
Line of credit, credit agreement		$ 800,000,000			$ 800,000,000.0
Credit Agreement 2015 | Revolving Credit Facility
Interest Expense, Debt [Abstract]
Line of credit, credit agreement			$ 800,000,000