Convertible Notes (Details)		3 Months Ended
	Mar. 27, 2018 USD ($) day $ / shares shares	Mar. 31, 2018 USD ($)
Debt Instrument [Line Items]
Conversion ratio	0.032343
Stock price conversion threshold, percentage	130.00%
Consecutive trading days | day	20
Threshold trading days	30
Trading price threshold, percentage	98.00%
Repurchase principal balance, percent	100.00%
Net carrying amount		$ 99,200,000
Interest expense		158,000
Amortization of debt issuance costs		6,000
Amortization of the debt discount		100,000
Interest Payable		52,000
Net proceeds from notes to fund Prepaid Forward	$ 45,100,000
Aggregate number of shares | shares	1,858,500
Unsecured obligations | 2.50% Convertible notes due 2023
Debt Instrument [Line Items]
Aggregate principal amount	$ 150,000,000
Interest rate	2.50%
Conversion multiple	$ 1,000
Initial conversion price (usd per share) | $ / shares	$ 30.92
Proceeds received	$ 150,000,000
Long-term debt	102,000,000
Equity component	$ 48,000,000
Effective interest rate	11.52%
Debt issuance costs	$ 4,300,000
Contractual term	5 years
Unamortized debt discount		$ 48,000,000
Unsecured obligations | 2.50% Convertible notes due 2023 | Long-term debt
Debt Instrument [Line Items]
Debt issuance costs	$ 2,900,000
Unamortized debt issuance cost	2,900,000
Unsecured obligations | 2.50% Convertible notes due 2023 | Additional paid-in capital
Debt Instrument [Line Items]
Debt issuance costs	$ 1,400,000