Summary Selected Quarterly Financial Data - Summary of Selected Consolidated Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 77,521	$ 69,815	$ 78,953	$ 71,361	$ 75,161	$ 68,773	$ 78,932	$ 70,165		$ 297,650	$ 293,031	$ 283,335
Income from operations	4,464	4,301	9,788	3,280	7,945	7,130	11,152	4,533		21,833	30,760	36,716
Net income	$ 2,161	$ 2,509	$ 6,185	$ 2,169	$ 4,477	$ 11,111	$ 7,584	$ 3,124	$ 10,863	$ 13,024	$ 26,296	$ 21,991
Basic income per common share	$ 0.11	$ 0.12	$ 0.29	$ 0.10	$ 0.20	$ 0.50	$ 0.34	$ 0.14		$ 0.62	$ 1.17	$ 0.97
Diluted income per common share	$ 0.11	$ 0.12	$ 0.28	$ 0.10	$ 0.20	$ 0.49	$ 0.33	$ 0.13		$ 0.61	$ 1.15	$ 0.95