Investment in Joint Venture - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Equity Method Investments [Line Items]
Cash dividends received, recorded as reduction in Company's investment in joint venture				$ 400,000	$ 0
Recognized gain from sale of joint venture		$ 6,300,000	$ 0	6,300,000	0
Tax expenses related to sale of joint venture		7,900,000	$ 5,500,000	$ 12,400,000	$ 10,800,000
Dowa Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Interest in joint venture, Sales percentage	50.00%
Proceed from sale of joint venture	$ 8,000,000
Recognized gain from sale of joint venture		6,300,000
Tax expenses related to sale of joint venture		$ 1,500,000