Sales Activity of Series D Preferred Shares (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Temporary Equity [Line Items]
Aggregate purchase price	$ 100,000
Initial value of warrants and investor SARs issued to-date	(21,805)
Costs incurred	(6,384)
Total discount	(28,189)
Discount amortization to-date	10,702
Carrying amount of Series D Preferred Shares	$ 82,513	$ 79,308