Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended					12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2017
Earnings Per Share, Diluted [Line Items]
Net income attributable to shareholders		$ 139,094	$ 53,653	$ 134,064	$ 99,722	$ 114,737	$ 402,176
Weighted average shares outstanding - basic		87,955				89,262
Net effect of various dilutive stock-based compensation awards		1,080				1,279
Weighted average shares outstanding - diluted		89,035				90,541
Net income per share:
Basic		$ 1.58				$ 1.29
Diluted	[1]	$ 1.56				$ 1.27
Stock Compensation Plan [Member]
Net income per share:
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		415				244

[1] Stock-based compensation awards for the issuance of 415 and 244 for the first quarter of 2018 and 2017, respectively, were excluded from the computation of net income per share on a diluted basis as their effect was anti-dilutive.