Earnings per Share - Schedule of Computation of Basic and Diluted Earnings per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Net Income	$ 9,012	$ 19,792	$ 28,737	$ 41,559
Noncontrolling interests	765	(249)	382	(78)
Net Income Attributable to Common Stockholders	$ 9,777	$ 19,543	$ 29,119	$ 41,481
Shares:
Basic: Weighted-average number of shares outstanding	8,889	9,133	8,927	9,125
Plus: Incremental shares from assumed conversion of dilutive instruments	148	192	167	218
Diluted: Weighted-average number of shares outstanding	9,037	9,325	9,094	9,343
Earnings per share - basic	$ 1.10	$ 2.14	$ 3.26	$ 4.55
Earnings per share - diluted	$ 1.08	$ 2.10	$ 3.20	$ 4.44