Convertible Notes (Details)		3 Months Ended		9 Months Ended
	Sep. 29, 2014 USD ($)	Sep. 30, 2017 USD ($) item $ / shares	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($)	Sep. 30, 2014 USD ($)
Long-term Debt		$ 140,400,000		$ 140,400,000
Convertible Debt, Fair Value Disclosures		751,400,000		751,400,000
Interest expense
Total interest expense		$ 4,424,000	$ 4,119,000	$ 13,117,000	$ 12,220,000
Convertible senior notes due October 2021
Principal	$ 201,300,000					$ 201,300,000
Capped call transactions payments	$ 20,800,000
Interest rate (as a percent)	3.00%					3.00%
Conversion price per share of convertible notes into common stock | $ / shares		$ 35.13		$ 35.13
Convertible notes conversion ratio per 1,000 principal		28.4627
Denominator Of Principal Amount Denomination For Conversion Into Common Stock		$ 1,000
Long-term Debt		140,400,000		$ 140,400,000
Convertible Debt, Fair Value Disclosures		751,400,000		751,400,000
Convertible debt outstanding
Principal	$ 201,300,000					$ 201,300,000
Interest expense
Contractual interest expense		1,509,000	1,509,000	4,528,000	4,528,000
Amortization of debt discount		2,779,000	2,460,000	8,172,000	7,236,000
Amortization of debt issuance costs		136,000	150,000	416,000	456,000
Total interest expense		$ 4,424,000	$ 4,119,000	$ 13,116,000	$ 12,220,000
Convertible senior notes due October 2021 | Conversion of convertible notes into common stock after December 31,2014
Convertible threshold trading days | item		20
Convertible threshold consecutive trading days | item		30
Minimum threshold percentage of stock price trigger		130.00%
Convertible senior notes due October 2021 | Conversion of convertible notes when common share trading price is less than 98% of target ratio
Convertible threshold trading days | item		5
Convertible threshold consecutive trading days | item		10
Denominator Of Principal Amount Denomination For Conversion Into Common Stock		$ 1,000
Threshold percentage forcing conversion when less than share price times conversion ratio		98.00%