Borrowings - 4.50% Convertible Senior Notes - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2013	Jul. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule Of Debt Instruments [Line Items]
Debt maturity date					Jul. 15, 2020
Interest expense			$ 4,476,000	$ 4,585,000	$ 13,524,000	$ 13,666,000
4.50% Convertible Senior Notes [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount		$ 125,000,000
Net proceeds from the debt issuance		$ 120,600,000
Interest rate (as a percent)	4.50%	4.50%	4.50%		4.50%
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible	30 days		30 days
Convertibility of debt, closing price of stock test, percentage of stock price to conversion price for the notes that must be exceeded	130.00%		130.00%
Number of consecutive business days immediately after any five consecutive trading day period during the note measurement period	5 days
Number of consecutive trading days before five consecutive business days during the note measurement period	5 days
Conversion ratio, principal amount	$ 1,000	$ 1,000
Conversion rate of common stock shares per $1,000 principal amount	160
Initial conversion price of shares (in dollars per share)	$ 6.25	$ 6.25
Underwriting discounts and commissions and offering expenses	$ 4,400,000
Interest expense			$ 3,400,000	$ 3,400,000	$ 10,300,000	$ 10,300,000
4.50% Convertible Senior Notes [Member] | Minimum [Member]
Schedule Of Debt Instruments [Line Items]
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible	20 days		20 days
4.50% Convertible Senior Notes [Member] | Maximum [Member]
Schedule Of Debt Instruments [Line Items]
Convertibility of debt, trading price of debt test, percentage of closing price of stock used in calculation	98.00%