Related-Party Transactions - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended	0 Months Ended	3 Months Ended	9 Months Ended			0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Mar. 31, 2014 Q1 2014 Declaration [Member]	Sep. 30, 2014 Q1 2014 Declaration [Member]	May 31, 2014 Q2 2014 Declaration [Member]	Sep. 30, 2014 Q2 2014 Declaration [Member]	Sep. 30, 2014 Q3 2014 Declaration [Member]	Sep. 30, 2014 Q3 2014 Declaration [Member]	Apr. 24, 2013 Blackstone and Affiliates [Member]	Sep. 30, 2014 Blackstone and Affiliates [Member]	Sep. 30, 2014 Blackstone and Affiliates [Member]	Sep. 30, 2013 Blackstone and Affiliates [Member]	Apr. 24, 2013 Blackstone and Affiliates [Member]	Apr. 01, 2014 Blackstone and Affiliates [Member] Q1 2014 Declaration [Member]	Jul. 01, 2014 Blackstone and Affiliates [Member] Q2 2014 Declaration [Member]	Oct. 06, 2014 Blackstone and Affiliates [Member] Q3 2014 Declaration [Member] Subsequent Events [Member]
Related Party Transaction [Line Items]
Advisory Agreement, fees												$ 0	$ 0	$ 2,799,000
Termination fee paid															46,300,000
Write-off of 2013 prepaid advisory fee											3,772,000
Termination of advisory agreement				50,072,000										50,072,000
Cash dividends declared per share	$ 0.21	$ 0.20	$ 0.62	$ 0.40	$ 0.20		$ 0.21		$ 0.21
Cash dividends declare date						2014-03		2014-05	2014-09	2014-09
Cash dividends record date						Mar. 20, 2014		Jun. 20, 2014		Sep. 29, 2014
Cash dividends paid date						Apr. 01, 2014		Jul. 01, 2014		Oct. 06, 2014
Dividends paid to stockholders			$ 53,639,000	$ 18,124,000												$ 7,849,000	$ 4,252,000	$ 4,095,000