Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 27, 2014	Jun. 28, 2014	Mar. 29, 2014	Sep. 28, 2013	Jun. 29, 2013	Mar. 30, 2013	Jun. 28, 2014	Jun. 29, 2013	Sep. 27, 2014	Sep. 28, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Amortization of actuarial loss included in net income (loss), tax expense (benefit)	$ 40	$ 48	$ 36	$ 102	$ 102	$ 102	$ 84	$ 204	$ 124	$ 306	$ 156	$ 408	$ 427
Actuarial gain (loss) arising during the period, tax expense (benefit)											$ 1,810	$ (1,737)	$ (300)