Senior Notes Due May 1, 2016 - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	0 Months Ended	6 Months Ended			0 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Senior Notes	Jun. 30, 2014 Senior Notes	Oct. 04, 2013 Senior Notes 5.75% Senior Notes	Jun. 30, 2014 Senior Notes 5.75% Senior Notes	Jun. 30, 2014 Senior Notes 5.75% Senior Notes Semi Annual Payment, First Payment	Jun. 30, 2014 Senior Notes 5.75% Senior Notes Semi Annual Payment, Second Payment	Oct. 04, 2013 Senior Notes 7.0% Senior Notes	Jun. 30, 2013 Senior Notes 7.0% Senior Notes	Jun. 30, 2014 Senior Notes 7.0% Senior Notes	Jun. 30, 2013 Senior Notes 7.0% Senior Notes
Debt Instrument [Line Items]
Principal amount of senior notes							$ 265,000,000
Interest rate stated on senior notes							5.75%						7.00%
Senior notes due date							Oct. 15, 2023						May 01, 2016
Net proceeds from issuance of senior notes							263,000,000
Unamortized discount					1,600,000	1,600,000
Outstanding principal amount of senior notes								263,400,000
Call premium on redemption of Senior Notes											17,900,000
Fair value of senior notes								291,000,000
Interest expense on senior notes												2,100,000		4,100,000
Effective interest rate related to senior notes								5.86%
Interest payment date on senior notes									--04-15	--10-15
Interest expense	$ 4,319,000	$ 2,052,000	$ 8,171,000	$ 4,103,000	$ 4,300,000	$ 8,200,000
Debt instrument, covenant compliance								As of June 30, 2014, the Company was in compliance with all such covenants.