Equity Transactions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		64 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016
Equity [Abstract]
Repurchases of common shares (in shares)	176,204	103,818	1,400,000
Weighted average purchase price per share (in $ per share)	$ 85.09	$ 134.81	$ 124.17
Total cost of treasury shares acquired	$ 15,000	$ 14,000	$ 172,600
Common stock available to repurchase (in shares)	1,300,000.0		1,300,000.0
Cash dividends declared per share (in $ per share)	$ 0.45	$ 0.45
Total cash dividends	$ 3,850	$ 4,095
Dividend, to be paid date	May 13, 2016
Dividend, record date	Apr. 29, 2016