Stockholder's Equity - Shares of Common Stock Issued During 2016 Under Employee Stock Purchase Plan (Detail) - $ / shares	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares available, Beginning balance			213,760	213,760
Shares issued during period (shares)	5,239	6,434	5,341
Shares available, Ending Balance	196,746			196,746
Shares issued during period (per share price)	$ 41.12	$ 33.78	$ 43.03