Stock-Based Compensation Plans - PSUA Activity (Detail) (Performance Shares, USD $)	12 Months Ended
	Dec. 31, 2014
Performance Shares
Summary of Performance Share Unit Awards outstanding, Number of Units
Outstanding, Beginning Balance	0
Granted	227,929	[1]
Vested	(92,077)	[2]
Forfeited	(1,511)
Outstanding, Ending Balance	134,341
Summary of Performance Share Unit Awards outstanding, Weighted Average Grant Date Fair Value
Outstanding, Beginning Balance, weighted average grant date fair value	$ 0
Granted, weighted average grant date fair value	$ 86.14	[1]
Vested, weighted average grant date fair value	$ 86.23	[2]
Forfeited, weighted average grant date fair value	$ 82.60
Outstanding, Ending Balance, weighted average grant date fair value	$ 86.11

[1] Amounts granted reflect the number of performance units granted. The actual payout of shares may be between zero percent and 150% of the performance units granted depending on the total shareholder return ranking compared to our peer companies at the vesting date.

[2] Primarily represents PSU awards granted to our prior executive chairman for the 2013 calendar year while he was a Range officer.