Stock-Based Compensation - Summary of Restricted Stock and Restricted Stock Units Granted (Detail) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Feb. 27, 2018	Feb. 21, 2017	Feb. 24, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares (in shares)				169,870	186,961	193,788
Assumed adjustment for performance objectives (in shares)				106,084	(35,073)	(58,056)
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Settlement of performance shares		119,896	159,020
Shares (in shares)				153,000	167,500	179,500
Price per share (in dollars per share)				$ 77.26	$ 50.64	$ 53.61
Assumed adjustment for performance objectives (in shares)				106,084	(35,073)	(58,056)
Aggregate value				$ 11,821	$ 8,482	$ 9,623
Percent vested				0.00%	0.00%	0.00%
Executive Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares (in shares)				0	0	0
Price per share (in dollars per share)				$ 0.00
Assumed adjustment for performance objectives (in shares)
Directors Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares (in shares)				9,135	12,549	6,648
Price per share (in dollars per share)				$ 73.92	$ 57.39	$ 54.16
Assumed adjustment for performance objectives (in shares)
Aggregate value				$ 675	$ 720	$ 360
Percent vested				100.00%	85.00%	100.00%
Directors Restricted Stock Units Including Dividend Equivalents
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares (in shares)				7,735	6,912	7,640
Price per share (in dollars per share)				$ 74.45	$ 56.74	$ 54.44
Aggregate value				$ 576	$ 392	$ 416
Percent vested				100.00%	100.00%	100.00%
Subsequent Event | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Settlement of performance shares	149,898