Earnings Per Share Earnings Per Share - Computation of Basic and Diluated Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerators:
Net income	$ 15,488	$ 16,050	$ 16,375	$ 13,820	$ 14,762	$ 15,162	$ 12,074	$ 9,567	$ 61,733	$ 51,565	$ 32,445
Denominators:
Basic weighted average common shares outstanding (in shares)	33,638,170	33,624,401	33,621,444	33,380,028	33,231,716	33,307,312	33,417,079	33,236,259	33,566,367	33,298,104	32,804,606
Dilutive effect of share based awards (in shares)									996,952	880,236	831,987
Diluted weighted average common shares outstanding (in shares)	34,714,308	34,675,485	34,510,400	34,351,657	34,272,731	34,180,635	34,207,973	34,051,971	34,563,319	34,178,340	33,636,593
Earnings per share:
Basic (in dollars per share)	$ 0.46	$ 0.48	$ 0.49	$ 0.41	$ 0.44	$ 0.46	$ 0.36	$ 0.29	$ 1.84	$ 1.55	$ 0.99
Diluted (in dollars per share)	$ 0.45	$ 0.46	$ 0.47	$ 0.40	$ 0.43	$ 0.44	$ 0.35	$ 0.28	$ 1.79	$ 1.51	$ 0.96
Weighted average common shares considered anti-dilutive in computing diluted earnings per share (in shares)									92,538	73,896	114,395