Common Stock - Additional Information (Detail) - USD ($)		3 Months Ended	6 Months Ended		12 Months Ended
	Mar. 10, 2015	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Value of common shares planning to sell			$ 22,760,000
Net proceeds to Company			$ 20,713,000	$ 237,000	$ 20,881,000	$ 515,000
Common stock issued through Stock Incentive Plan, Restricted Stock/Unit Plan, and Management Incentive Plan			145,000
BNY Mellon Capital Markets, LLC [Member]
Common stock sold through agent		180,247	372,509
Common stock weighted average price		$ 53.90
Net proceeds to Company		$ 9,618,188	$ 20,557,144
Agent commissions		97,154	207,649
Common stock available for sale under the program		$ 79,235,207	$ 79,235,207		$ 79,235,207
Maximum [Member]
Value of common shares planning to sell	$ 100,000,000