XML 153 R137.htm IDEA: XBRL DOCUMENT v3.3.1.900
Stockholders' Equity - Summary of Assumptions Used to Calculate the Grant Date Fair Value Based on Total Shareholder Return (Detail) - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Number of units granted 71,893 101,062 51,321
PSUs – Total Shareholder Return [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Number of units granted 65,796 129,150 242,988
Weighted average fair value on grant date $ 59.91 $ 43.13 $ 28.64
Expected Price volatility 29.90% 32.90% 31.40%
Risk-free interest rate 1.05% 0.63% 0.42%