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Fair Value Measurement - Additional Information (Detail) (USD $)	12 Months Ended	3 Months Ended
	Dec. 31, 2014	Mar. 31, 2014	Mar. 31, 2015
5.75% Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate stated on senior notes			5.75%
Senior notes due date	Oct. 15, 2023
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Level 3 assets			0
Transfers from Level 3 to Level 2		$ 4,400,000